Optical sensing performance of under-screen optical sensor module for on-screen fingerprint sensing

ABSTRACT

Devices and optical sensor modules are provided for provide on-screen optical sensing of fingerprints by using an under-screen optical sensor module that captures and detects returned light that is emitted by the display screen for displaying images and that is reflected back by the top surface of the screen assembly. Optical collimators are provided in the under-screen optical sensor module to enhance the optical imaging performance. Techniques for reducing the environmental light in the optical sensing are provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/862,590, filed on Jan. 4, 2018, which claims the benefits andpriorities of U.S. Provisional Patent Application No. 62/442,387, filedon Jan. 4, 2017, and U.S. Provisional Patent Application No. 62/452,938,filed on Jan. 31, 2017.

U.S. patent application Ser. No. 15/862,590 further claims the benefitsand priority of, and is a continuation-in-part application of, U.S.patent application Ser. No. 15/616,856, filed on Jun. 7, 2017, whichclaims the benefits and priorities of U.S. Provisional PatentApplication No. 62/347,073, filed on Jun. 7, 2016; U.S. ProvisionalPatent Application No. 62/363,832, filed on Jul. 18, 2016; and U.S.Provisional Patent Application No. 62/363,823, filed on Jul. 18, 2016.

Furthermore, U.S. patent application Ser. No. 15/616,856 claims thebenefits and priority of, and is a continuation-in-part application of,International Patent Application No. PCT/US2016/038445, filed on Jun.20, 2016, which claims the benefits and priority of U.S. ProvisionalPatent Application No. 62/181,718, filed on Jun. 18, 2015.

In addition, U.S. patent application Ser. No. 15/862,590 claims thebenefits and priority of, and is a continuation-in-part application of,U.S. patent application Ser. No. 15/421,249, filed on Jan. 31, 2017,which claims the benefits and priorities of U.S. Provisional PatentApplication No. 62/289,328, filed on Jan. 31, 2016; U.S. ProvisionalPatent Application No. 62/330,833, filed on May 2, 2016; and U.S.Provisional Patent Application No. 62/347,073, filed on Jun. 7, 2016.

The entire contents of the before-mentioned patent applications areincorporated by reference as part of the disclosure of this document.

TECHNICAL FIELD

This patent document relates to sensing of fingerprints and performingone or more sensing operations of other parameter measurements of inelectronic devices or systems, including portable devices such as amobile device or a wearable device and larger systems.

BACKGROUND

Various sensors can be implemented in electronic devices or systems toprovide certain desired functions. There is an increasing need forsecuring access to computers and computer-controlled devices or systemswhere only authorized users be identified and be distinguished fromnon-authorized users.

For example, mobile phones, digital cameras, tablet PCs, notebookcomputers and other portable electronic devices have become more andmore popular in personal, commercial and governmental uses. Portableelectronic devices for personal use may be equipped with one or moresecurity mechanisms to protect the user's privacy.

For another example, a computer or a computer-controlled device orsystem for an organization or enterprise may be secured to allow onlyauthorized personnel to access to protect the information or the use ofthe device or system for the organization or enterprise.

The information stored in portable devices and computer-controlleddatabases, devices or systems, may be of certain characteristics thatshould be secured. For example, the stored information may be personalin nature, such as personal contacts or phonebook, personal photos,personal health information or other personal information, orconfidential information for proprietary use by an organization orenterprise, such as business financial information, employee data, tradesecrets and other proprietary information. If the security of the accessto the electronic device or system is compromised, the data may beaccessed by others that are not authorized to gain the access, causingloss of privacy of individuals or loss of valuable confidentialinformation. Beyond security of information, securing access tocomputers and computer-controlled devices or systems also allowsafeguard of the use of devices or systems that are controlled bycomputers or computer processors such as computer-controlled automobilesand other systems such as ATMs.

Security access to a device such as a mobile device or a system such asan electronic database and a computer-controlled system can be achievedin different ways such as using user passwords. A password, however, maybe easily to be spread or obtained and this nature of passwords canreduce the level of the security. Moreover, a user needs to remember apassword to use password-protected electronic devices or systems, and,if the user forgets the password, the user needs to undertake certainpassword recovery procedures to get authenticated or otherwise regainthe access to the device. Unfortunately, in various circumstances, suchpassword recovery processes may be burdensome to users and have variouspractical limitations and inconveniences.

The personal fingerprint identification can be utilized to achieve theuser authentication for enhancing the data security while mitigatingcertain undesired effects associated with passwords.

Electronic devices or systems, including portable or mobile computingdevices, may employ user authentication mechanisms to protect personalor other confidential data and prevent unauthorized access. Userauthentication on an electronic device or system may be carried outthrough one or multiple forms of biometric identifiers, which can beused alone or in addition to conventional password authenticationmethods. One form of biometric identifiers is a person's fingerprintpattern. A fingerprint sensor can be built into an electronic device orsystem to read a user's fingerprint pattern as part of theauthentication process so that the device or system can only be unlockedby an authorized user through authentication of the authorized user'sfingerprint pattern.

SUMMARY

The sensor technology and examples of implementations of the sensortechnology described in this patent document provide an optical sensormodule that uses light from a display screen to perform one or moresensing operations based on optical sensing of such light. A suitabledisplay screen for implementing the disclosed optical sensor technologycan be based on various display technologies or configurations,including, a display screen having light emitting display pixels withoutusing backlight where each individual pixel generates light for formingpart of a display image on the screen such as an organic light emittingdiode (OLED) display screens or electroluminescent display screens. Thedisclosed optical sensor technology may also be adapted for use withother display screens, such as LCD display screens. In applications, thedisclosed technology can be implemented to provide on-screen opticalsensing of fingerprints by using an under-screen optical sensor modulethat captures and detects returned light that is emitted by the displayscreen for displaying images and that is reflected back by the topsurface of the screen assembly.

In one aspect, the disclosed technology can be implemented to provide anelectronic device capable of detecting a fingerprint by optical sensingto include a display panel that includes light emitting display pixels,each pixel operable to emit light for forming a portion of a displayimage; a top transparent layer formed over the display panel as aninterface for being touched by a user and for transmitting the lightfrom the display panel to display images; and an optical sensor modulelocated below the display panel to receive light that is emitted by atleast a portion of the light emitting display pixels and is returnedfrom the top transparent layer to detect a fingerprint. The opticalsensor module includes an optical sensor array of optical detectors andan array of optical collimators located between the display panel andthe optical sensor array to collect the returned light from the displaypanel and to separate light from different locations in the toptransparent layer while directing the collected returned light to theoptical sensor array. The array of optical collimators is spaced fromthe optical sensor array to effectuate a pinhole camera effect thatenhances an optical imaging resolution of the optical sensor array. Thisdevice further includes one or more optical filters placed between a topsurface of the top transparent layer and the optical sensor array of theoptical sensor module to block or reduce an amount of environmentallight from entering the optical sensor array.

In another aspect, the disclosed technology can be implemented toprovide an electronic device capable of detecting a fingerprint byoptical sensing that includes a device screen that provides touchsensing operations and includes a display panel structure having lightemitting display pixels, each pixel operable to emit light for forming aportion of a display image; a top transparent layer formed over thedevice screen as an interface for being touched by a user for the touchsensing operations and for transmitting the light from the displaystructure to display images to a user; one or more extra illuminationlight sources located to provide additional illumination light to thetop transparent layer formed over the device screen as the interface forbeing touched by a user; and an optical sensor module located below thedisplay panel structure to receive light that is emitted by at least aportion of the light emitting display pixels of the display structureand by the one or more extra illumination light sources and is returnedfrom the top transparent layer to detect a fingerprint. The opticalsensor module includes an optical sensor array that detects an image inthe received light in the optical sensor module.

In yet another aspect, the disclosed technology can be implemented toprovide a method for operating an electronic device capable of detectinga fingerprint by optical sensing by operating an optical sensor modulelocated below a touch display panel, that provides touch sensingoperations for the device, to produce probe light to the illuminate atop transparent layer of the touch display panel to operate an opticalsensor array inside the optical sensor module to obtain a first imagefrom returned probe light from the top transparent layer. This methodincludes operating the optical sensor array inside the optical sensormodule, while turning off the probe light, to obtain a second imageunder illumination with only environmental light without illuminatingthe top transparent layer of the touch display panel with any probelight; and processing the first image and the second image to remove aneffect from the environmental light in an imaging operation of thedevice.

Those and other aspects and their implementations are described ingreater detail in the drawings, the description and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example of a system with a fingerprintsensing module which can be implemented to include an opticalfingerprint sensor disclosed in this document.

FIGS. 2A and 2B illustrate one exemplary implementation of an electronicdevice 200 having a touch sensing display screen assembly and an opticalsensor module positioned underneath the touch sensing display screenassembly.

FIGS. 2C and 2D illustrate an example of a device that implements theoptical sensor module in FIGS. 2A and 2B.

FIG. 3 illustrates one example of an OLED display and touch sensingassembly suitable for implementing the disclosed optical fingerprintsensing technology.

FIGS. 4A and 4B show an example of one implementation of an opticalsensor module under the display screen assembly for implementing thedesign in FIGS. 2A and 2B.

FIGS. 5A and 5B illustrate signal generation for the returned light fromthe sensing zone on the top sensing surface under two different opticalconditions to facilitate the understanding of the operation of theunder-screen optical sensor module.

FIGS. 6A-6C, 7, 8A-8B, 9, and 10A-10B show example designs ofunder-screen optical sensor modules.

FIG. 11 shows imaging of the fingerprint sensing area on the toptransparent layer via an imaging module under different tilingconditions where an imaging device images the fingerprint sensing areaonto an optical sensor array and the imaging device may be opticallytransmissive or optically reflective.

FIG. 12 shows an example of an operation of the fingerprint sensor forreducing or eliminating undesired contributions from the backgroundlight in fingerprint sensing.

FIG. 13 shows a process for operating an under-screen optical sensormodule for capturing a fingerprint pattern.

FIGS. 14A, 14B and FIG. 15 show an example of an operation process fordetermining whether an object in contact with the OLED display screen ispart of a finger of a live person by operating the OLED pixels toilluminate the finger in two different light colors.

FIG. 16 shows an example of a standard calibration pattern produced bythe OLED display for calibrating the imaging sensing signals output bythe optical sensor array for fingerprint sensing.

FIGS. 17A-17B, 18 and 19A-19C show optical collimator designs foroptical fingerprint sensing suitable for implementing the disclosedunder-screen optical sensor module technology.

FIGS. 20, 21A, 21B, 22A, and 22B illustrate examples of various designsfor fingerprint sensing using an under-screen optical sensor moduleusing an array of optical collimators or pinholes for directing signallight carrying fingerprint information to the optical sensor array.

FIGS. 23 and 24 show examples of under-screen optical sensor moduleswith optical collimators.

FIG. 25 shows an example an optical collimator array with opticalfiltering to reduce background light that reaches the photodetectorarray in the under-screen optical sensor module.

FIGS. 26A, 26B, 27 and 28 show examples of optical collimator designsfor the optical sensing under the OLED display screen.

FIGS. 29, 30, 31A and 31B illustrate improved optical imaging resolutionbased on a pinhole camera effect in designing the optical sensor module.

FIG. 32 includes FIGS. 32A and 32B and shows an example of an opticalfingerprint senor under an OLED display panel having an opticaldeflection or diffraction device or layer.

FIG. 33 shows two different fingerprint patterns of the same fingerunder different press forces: the lightly pressed fingerprint 2301 andthe heavily pressed fingerprint 3303.

FIG. 34 shows an example of the optical transmission spectral profilesof a typical human thumb and litter finger at several different opticalwavelengths from around 525 nm to around 940 nm.

FIG. 35 illustrates influences of the background light in an example ofan under-screen optical sensor module.

FIG. 36 shows an example of a design algorithm for designing the opticalfiltering in an under-screen optical sensor module for reducingbackground light.

FIG. 37 shows two examples in FIGS. 37A and 37B for an under-screenoptical sensor module having an optical collimator array or an opticalpinhole array before the optical detector array as part of the receivingoptics with a small optical numerical aperture to reduce the backgroundlight that enters the optical detector array.

FIG. 38 illustrates an example of a sensor initialization process thatmeasures a baseline background level at the optical sensor array eachtime a fingerprint is obtained.

FIGS. 39 and 40 show behaviors different optical signals in an exampleof an under-screen optical sensor module having extra illumination lightsources to supplement the fingerprint sensing illumination by the OLEDdisplay light.

FIG. 41 shows an example of a design algorithm for designing the opticalfiltering in an under-screen optical sensor module for reducingbackground light in the presence of extra light sources for opticalsensing.

DETAILED DESCRIPTION

Electronic devices or systems may be equipped with fingerprintauthentication mechanisms to improve the security for accessing thedevices. Such electronic devices or system may include, portable ormobile computing devices, e.g., smartphones, tablet computers,wrist-worn devices and other wearable or portable devices, largerelectronic devices or systems, e.g., personal computers in portableforms or desktop forms, ATMs, various terminals to various electronicsystems, databases, or information systems for commercial orgovernmental uses, motorized transportation systems includingautomobiles, boats, trains, aircraft and others.

Fingerprint sensing is useful in mobile applications and otherapplications that use or require secure access. For example, fingerprintsensing can be used to provide secure access to a mobile device andsecure financial transactions including online purchases. It isdesirable to include robust and reliable fingerprint sensing suitablefor mobile devices and other applications. In mobile, portable orwearable devices, it is desirable for fingerprint sensors to minimize oreliminate the footprint for fingerprint sensing given the limited spaceon those devices, especially considering the demands for a maximumdisplay area on a given device.

The light produced by a display screen for displaying images can passthrough the top surface of the display screen in order to be viewed by auser. A finger can touch the top surface and thus interacts with thelight at the top surface to cause the reflected or scattered light atthe surface area of the touch to carry spatial image information of thefinger to return to the display panel underneath the top surface. Intouch sensing display devices, the top surface is the touch sensinginterface with the user and this interaction between the light fordisplaying images and the user finger or hand constantly occurs but suchinformation-carrying light returning back to the display panel islargely wasted and is not used in most touch sensing devices. In variousmobile or portable devices with touch sensing displays and fingerprintsensing functions, a fingerprint sensor tends to be a separate devicefrom the display screen, either placed on the same surface of thedisplay screen at a location outside the display screen area such as inthe popular Apple iPhones and recent Samsung Galaxy smartphones, orplaced on the backside of a smartphone, such as some new models of smartphones by Huawei, Lenovo, Xiaomi or Google, to avoid taking up valuablespace for placing a large display screen on the front side. Thosefingerprint sensors are separate devices from the display screens andthus need to be compact to save space for display and other functionswhile still providing reliable and fast fingerprint sensing with aspatial image resolution above a certain acceptable level. However, theneed to be compact and small and the need to provide a high spatialimage resolution in capturing a fingerprint pattern are in directconflict with each other in many fingerprint sensors because a highspatial image resolution in capturing a fingerprint pattern in based onvarious suitable fingerprint sensing technologies (e.g., capacitivetouch sensing or optical imaging) requires a large sensor area with alarge number of sensing pixels.

The optical sensor technology disclosed herein uses the light fordisplaying images in a display screen that is returned from the topsurface of the device display assembly for fingerprint sensing and othersensing operations. The returned light carries information of an objectin touch with the top surface (e.g., a finger) and the capturing anddetecting this returned light constitute part of the designconsiderations in implementing a particular optical sensor modulelocated underneath the display screen. Because the top surface of thetouch screen assembly is used as a fingerprint sensing area, the opticalimage of this touched area should be captured by an optical imagingsensor array inside the optical sensor module with a high image fidelityto the original fingerprint for robust fingerprint sensing. The opticalsensor module can be designed to achieve this desired optical imaging byproperly configuring optical elements for capturing and detecting thereturned light.

The disclosed technology can be implemented to provide devices, systems,and techniques that perform optical sensing of human fingerprints andauthentication for authenticating an access attempt to a lockedcomputer-controlled device such as a mobile device or acomputer-controlled system, that is equipped with a fingerprintdetection module. The disclosed technology can be used for securingaccess to various electronic devices and systems, including portable ormobile computing devices such as laptops, tablets, smartphones, andgaming devices, and other electronic devices or systems such aselectronic databases, automobiles, bank ATMs, etc.

The optical sensor technology disclosed here can be implemented todetect a portion of the light that is used for displaying images in adisplay screen where such a portion of the light for the display screenmay be the scattered light, reflected light or some stray light. Forexample, in some implementations of the disclosed optical sensortechnology for an OLED display screen or another display screen havinglight emitting display pixels without using backlight, the image lightproduced by the OLED display screen, at or near the OLED displayscreen's top surface, may be reflected or scattered back into the OLEDdisplay screen as returned light when encountering an object such as auser finger or palm, or a user pointer device like a stylus. Suchreturned light can be captured for performing one or more opticalsensing operations using the disclosed optical sensor technology. Due tothe use of the light from OLED display screen's own OLED pixels foroptical sensing, an optical sensor module based on the disclosed opticalsensor technology can be, in some implementations, specially designed tobe integrated to the OLED display screen in a way that maintains thedisplay operations and functions of the OLED display screen withoutinterference while providing optical sensing operations and functions toenhance overall functionality, device integration and user experience ofthe electronic device such as a smart phone or other mobile/wearabledevice or other forms of electronic devices or systems.

For example, an optical sensor module based on the disclosed opticalsensor technology can be coupled to a display screen having lightemitting display pixels without using backlight (e.g., an OLED displayscreen) to sense a fingerprint of a person by using the above describedreturned light from the light produced by OLED display screen. Inoperation, a person's finger, either in direct touch with the OLEDdisplay screen or in a near proximity of the OLED display screen, canproduce the returned light back into the OLED display screen whilecarrying information of a portion of the finger illuminated by the lightoutput by the OLED display screen. Such information may include, e.g.,the spatial pattern and locations of the ridges and valleys of theilluminated portion of the finger. Accordingly, the optical sensormodule can be integrated to capture at least a portion of such returnedlight to detect the spatial pattern and locations of the ridges andvalleys of the illuminated portion of the finger by optical imaging andoptical detection operations. The detected spatial pattern and locationsof the ridges and valleys of the illuminated portion of the finger canthen be processed to construct a fingerprint pattern and to performfingerprint identification, e.g., comparing with a stored authorizeduser fingerprint pattern to determine whether the detected fingerprintis a match as part of a user authentication and device access process.This optical sensing based fingerprint detection by using the disclosedoptical sensor technology uses the OLED display screens as an opticalsensing platform and can be used to replace existing capacitivefingerprint sensors or other fingerprint sensors that are basicallyself-contained sensors as “add-on” components without using light fromdisplay screens or using the display screens for fingerprint sensing formobile phones, tablets and other electronic devices.

The disclosed optical sensor technology can be implemented in ways thatuse a display screen having light emitting display pixels (e.g., an OLEDdisplay screen) as an optical sensing platform by using the lightemitted from the display pixels of the OLED display screens forperforming fingerprint sensing or other optical sensing functions aftersuch emitted light interacts with an area on the top touch surfacetouched by a finger. This intimate relationship between the disclosedoptical sensor technology and the OLED display screen provides a uniqueopportunity for using an optical sensor module based on the disclosedoptical sensor technology to provide both (1) additional optical sensingfunctions and (2) useful operations or control features in connectionwith the touch sensing aspect of the OLED display screen.

Notably, in some implementations, an optical sensor module based on thedisclosed optical sensor technology can be coupled to the backside ofthe OLED display screen without requiring a designated area on thedisplay surface side of the OLED display screen that would occupy avaluable device surface real estate in some electronic devices such as asmartphone, a tablet or a wearable device where the exterior surfacearea is limited. Such an optical sensor module can be placed under theOLED display screen that vertically overlaps with the display screenarea, and, from the user's perspective, the optical sensor module ishidden behind the display screen area. In addition, because the opticalsensing of such an optical sensor module is by detecting the light thatis emitted by the OLED display screen and is returned from the topsurface of the display area, the disclosed optical sensor module doesnot require a special sensing port or sensing area that is separate fromthe display screen area. Accordingly, different from fingerprint sensorsin other designs, including, e.g., Apple's iPhone/iPad devices orSamsung Galaxy smartphone models where the fingerprint sensor is locatedat a particular fingerprint sensor area or port (e.g., the home button)on the same surface of the display screen but located in a designatednon-displaying zone that is outside the display screen area, the opticalsensor module based on the disclosed optical sensor technology can beimplemented in ways that would allow fingerprint sensing to be performedat a location on the OLED display screen by using unique optical sensingdesigns to route the returned light from the finger into an opticalsensor and by providing proper optical imaging mechanism to achieve highresolution optical imaging sensing. In this regard, the disclosedoptical sensor technology can be implemented to provide a uniqueon-screen fingerprint sensing configuration by using the same top touchsensing surface that displays images and provides the touch sensingoperations without a separate fingerprint sensing area or port outsidethe display screen area.

Regarding the additional optical sensing functions beyond fingerprintdetection, the optical sensing may be used to measure other parameters.For example, the disclosed optical sensor technology can measure apattern of a palm of a person given the large touch area available overthe entire OLED display screen (in contrast, some designated fingerprintsensors such as the fingerprint senor in the home button of Apple'siPhone/iPad devices have a rather small and designated off-screenfingerprint sensing area that is highly limited in the sensing area sizethat may not be suitable for sensing large patterns). For yet anotherexample, the disclosed optical sensor technology can be used not only touse optical sensing to capture and detect a pattern of a finger or palmthat is associated with a person, but also to use optical sensing orother sensing mechanisms to detect whether the captured or detectedpattern of a fingerprint or palm is from a live person's hand by a “livefinger” detection mechanism, which may be based on, for example, thedifferent optical absorption behaviors of the blood at different opticalwavelengths, the fact that a live person's finger tends to be moving orstretching due to the person's natural movement or motion (eitherintended or unintended) or pulsing when the blood flows through theperson's body in connection with the heartbeat. In one implementation,the optical sensor module can detect a change in the returned light froma finger or palm due to the heartbeat/blood flow change and thus todetect whether there is a live heartbeat in the object presented as afinger or palm. The user authentication can be based on the combinationof the both the optical sensing of the fingerprint/palm pattern and thepositive determination of the presence of a live person to enhance theaccess control. For yet another example, the optical sensor module mayinclude a sensing function for measuring a glucose level or a degree ofoxygen saturation based on optical sensing in the returned light from afinger or palm. As yet another example, as a person touches the OLEDdisplay screen, a change in the touching force can be reflected in oneor more ways, including fingerprint pattern deforming, a change in thecontacting area between the finger and the screen surface, fingerprintridge widening, or a blood flow dynamics change. Those and other changescan be measured by optical sensing based on the disclosed optical sensortechnology and can be used to calculate the touch force. This touchforce sensing can be used to add more functions to the optical sensormodule beyond the fingerprint sensing.

With respect to useful operations or control features in connection withthe touch sensing aspect of the OLED display screen, the disclosedoptical sensor technology can provide triggering functions or additionalfunctions based on one or more sensing results from the optical sensormodule to perform certain operations in connection with the touchsensing control over the OLED display screen. For example, the opticalproperty of a finger skin (e.g., the index of refraction) tends to bedifferent from other artificial objects. Based on this, the opticalsensor module may be designed to selectively receive and detect returnedlight that is caused by a finger in touch with the surface of the OLEDdisplay screen while returned light caused by other objects would not bedetected by the optical sensor module. This object-selective opticaldetection can be used to provide useful user controls by touch sensing,such as waking up the smartphone or device only by a touch via aperson's finger or palm while touches by other objects would not causethe device to wake up for energy efficient operations and to prolong thebattery use. This operation can be implemented by a control based on theoutput of the optical sensor module to control the waking up circuitryoperation of the OLED display screen which, most of the OLED pixels areput in a “sleep” mode by being turned off without emitting light whilepart of the OLED pixels in the OLED display screen are turned on in aflash mode to intermittently emit flash light to the screen surface forsensing any touch by a person's finger or palm. Another “sleep” modeconfiguration can be achieved by using one or more extra LED lightsources built into the optical sensor module to produce the “sleep” modewake-up sensing light flashes where all the OLED pixels are turned offduring the sleep mode so that the optical sensor module can detectreturned light of such wake-up sensing light caused by the finger touchon the OLED display screen and, upon a positive detection, the OLEDpixels on the OLED display screen are turned on or “woken up”. In someimplementations, the wake-up sensing light can be in the infraredinvisible spectral range so a user will not experience any visual of aflash light. For another example, the fingerprint sensing by the opticalsensor module is based on sensing of the returned light from the surfaceof the OLED display screen in the course of the normal OLED displayscreen operation, the OLED display screen operation can be controlled toprovide an improved fingerprint sensing by eliminating background lightfor optical sensing of the fingerprint. In one implementation, forexample, each display scan frame generates a frame of fingerprintsignals. If, two frames of fingerprint signals with the display aregenerated in one frame when the OLED display screen is turned on and inthe other frame when the OLED display screen is turned off, thesubtraction between those two frames of signals can be used to reducethe ambient background light influence. By operating the fingerprintsensing frame rate is at one half of the display frame rate in someimplementations, the background light noise in fingerprint sensing canbe reduced.

As discussed above, an optical sensor module based on the disclosedoptical sensor technology can be coupled to the backside of the OLEDdisplay screen without requiring creation of a designated area on thesurface side of the OLED display screen that would occupy a valuabledevice surface real estate in some electronic devices such as asmartphone, a tablet or a wearable device. This aspect of the disclosedtechnology can be used to provide certain advantages or benefits in bothdevice designs and product integration or manufacturing.

In some implementations, an optical sensor module based on the disclosedoptical sensor technology can be configured as a non-invasive modulethat can be easily integrated to a display screen having light emittingdisplay pixels (e.g., an OLED display screen) without requiring changingthe design of the OLED display screen for providing a desired opticalsensing function such as fingerprint sensing. In this regard, an opticalsensor module based on the disclosed optical sensor technology can beindependent from the design of a particular OLED display screen designdue to the nature of the optical sensor module: the optical sensing ofsuch an optical sensor module is by detecting the light that is emittedby the OLED display screen and is returned from the top surface of thedisplay area, and the disclosed optical sensor module is coupled to thebackside of the OLED display screen as an under-screen optical sensormodule for receiving the returned light from the top surface of thedisplay area and thus does not require a special sensing port or sensingarea that is separate from the display screen area. Accordingly, such anunder-screen optical sensor module can be used to combine with OLEDdisplay screens to provide optical fingerprint sensing and other sensorfunctions on an OLED display screen without using a specially designedOLED display screen with hardware especially designed for providing suchoptical sensing. This aspect of the disclosed optical sensor technologyenables a wide range of OLED display screens in smartphones, tablets orother electronic devices with enhanced functions from the opticalsensing of the disclosed optical sensor technology.

For example, for an existing phone assembly design that does not providea separate fingerprint sensor as in certain Apple iPhones or SamsungGalaxy models, such an existing phone assembly design can integrate theunder-screen optical sensor module as disclosed herein without changingthe touch sensing-display screen assembly to provide an added on-screenfingerprint sensing function. Because the disclosed optical sensing doesnot require a separate designated sensing area or port as in the case ofcertain Apple iPhones/Samsung Galaxy phones with a front fingerprintsenor outside the display screen area, or some smartphones with adesignated rear fingerprint sensor on the backside like in some modelsby Huawei, Xiaomi, Google or Lenovo, the integration of the on-screenfingerprint sensing disclosed herein does not require a substantialchange to the existing phone assembly design or the touch sensingdisplay module that has both the touch sensing layers and the displaylayers. Based on the disclosed optical sensing technology in thisdocument, no external sensing port and no extern hardware button areneeded on the exterior of a device are needed for adding the disclosedoptical sensor module for fingerprint sensing. The added optical sensormodule and the related circuitry are under the display screen inside thephone housing and the fingerprint sensing can be conveniently performedon the same touch sensing surface for the touch screen.

For another example, due to the above described nature of the opticalsensor module for fingerprint sensing, a smartphone that integrates suchan optical sensor module can be updated with improved designs, functionsand integration mechanism without affecting or burdening the design ormanufacturing of the OLED display screens to provide desired flexibilityto device manufacturing and improvements/upgrades in product cycleswhile maintaining the availability of newer versions of optical sensingfunctions to smartphones, tablets or other electronic devices using OLEDdisplay screens. Specifically, the touch sensing layers or the OLEDdisplay layers may be updated in the next product release without addingany significant hardware change for the fingerprint sensing featureusing the disclosed under-screen optical sensor module. Also, improvedon-screen optical sensing for fingerprint sensing or other opticalsensing functions by such an optical sensor module can be added to a newproduct release by using a new version of the under-screen opticalsensor module without requiring significant changes to the phoneassembly designs, including adding additional optical sensing functions.

The above and other features of the disclosed optical sensor technologycan be implemented to provide a new generation of electronic deviceswith improved fingerprint sensing and other sensing functions,especially for smartphones, tablets and other electronic devices withdisplay screens having light emitting display pixels without usingbacklight (e.g., an OLED display screen) to provide various touchsensing operations and functions and to enhance the user experience insuch devices.

In practical applications, the performance of optical sensing forfingerprint sensing and other sensing functions in an electronic deviceequipped with optical fingerprint sensing may be degraded by thepresence of undesired background light from the environment where aportion of the background light may enter the optical sensor module.Such background light causes the optical detectors in the optical sensormodule to produce a noise signal that undesirable reduces the signal tonoise ratio of the optical fingerprint sensing detection. In someconditions, such background noise can be high to a degree that mayoverwhelm the signal level of the useful signal that carries the opticalfingerprint information or other useful information (e.g., biometricinformation) and could potentially cause unreliable optical sensingoperation or even malfunction of the optical sensing. For example, oneof sources for the undesired background light at the optical sensormodule may be from the daylight from the sun and the impact of thesunlight can be particularly problematic for outdoor operations or in asheltered environment with strong sunlight. For another example, otherlight sources present at locations at or near the location of the devicewith the disclosed optical fingerprint sensing may also lead to theundesired background light at the optical sensor module.

The undesired impact of the background light at the optical sensormodule may be mitigated by reducing the amount of the undesiredbackground light that can enter the optical sensor module, enhancing theoptical signal level of the optical sensing signal carrying thefingerprint or other useful information beyond the signal level by usingthe returned OLED display light, or a combination of both backgroundreduction and enhancing optical sensing signal level. Inimplementations, the background reduction can be achieved by using oneor more optical filtering mechanisms in connection with the under-screenoptical sensor module. In enhancing the optical signal level of theoptical sensing signal carrying the fingerprint or other usefulinformation, one or more extra illumination light sources may be addedto the device to provide additional optical illumination light beyondthe signal level caused by the returned OLED display light.

In the following sections, FIGS. 1-33 and associated textual descriptionfirst explain examples of various designs for an under-screen opticalsensor module for collecting an optical signal to the optical detectorsand providing desired optical imaging such as a sufficient imagingresolution by implementing at least one imaging lens or an array ofcollimators or pinholes. Specific examples of implementing backgroundlight filtering or adding extra illumination light for optical sensingare provided below with reference to the text and drawings in connectionwith FIGS. 1-41.

In implementations of the disclosed technical features, additionalsensing functions or sensing modules, such as a biomedical sensor, e.g.,a heartbeat sensor in wearable devices like wrist band devices orwatches, may be provided. In general, different sensors can be providedin electronic devices or systems to achieve different sensing operationsand functions.

FIG. 1 is a block diagram of an example of a system 180 with afingerprint sensing module 180 including a fingerprint sensor 181 whichcan be implemented to include an optical fingerprint sensor based on theoptical sensing of fingerprints as disclosed in this document. Thesystem 180 includes a fingerprint sensor control circuit 184, and adigital processor 186 which may include one or more processors forprocessing fingerprint patterns and determining whether an inputfingerprint pattern is one for an authorized user. The fingerprintsensing system 180 uses the fingerprint sensor 181 to obtain afingerprint and compares the obtained fingerprint to a storedfingerprint to enable or disable functionality in a device or system 188that is secured by the fingerprint sensing system 180. In operation, theaccess to the device 188 is controlled by the fingerprint processingprocessor 186 based on whether the captured user fingerprint is from anauthorized user. As illustrated, the fingerprint sensor 181 may includemultiple fingerprint sensing pixels such as pixels 182A-182E thatcollectively represent at least a portion of a fingerprint. For example,the fingerprint sensing system 180 may be implemented at an ATM as thesystem 188 to determine the fingerprint of a customer requesting toaccess funds or other transactions. Based on a comparison of thecustomer's fingerprint obtained from the fingerprint sensor 181 to oneor more stored fingerprints, the fingerprint sensing system 180 may,upon a positive identification, causes the ATM system 188 to grant therequested access to the user account, or, upon a negativeidentification, may deny the access. For another example, the device orsystem 188 may be a smartphone or a portable device and the fingerprintsensing system 180 is a module integrated to the device 188. For anotherexample, the device or system 188 may be a gate or secured entrance to afacility or home that uses the fingerprint sensor 181 to grant or denyentrance. For yet another example, the device or system 188 may be anautomobile or other vehicle that uses the fingerprint sensor 181 to linkto the start of the engine and to identify whether a person isauthorized to operate the automobile or vehicle.

As a specific example, FIGS. 2A and 2B illustrate one exemplaryimplementation of an electronic device 200 having a touch sensingdisplay screen assembly and an optical sensor module positionedunderneath the touch sensing display screen assembly. In this particularexample, the display technology can be implemented by an OLED displayscreen or another display screen having light emitting display pixelswithout using backlight. The electronic device 200 can be a portabledevice such as a smartphone or a tablet and can be the device 188 asshown in FIG. 1.

FIG. 2A shows the front side of the device 200 which may resemble somefeatures in some existing smartphones or tablets. The device screen ison the front side of the device 200 occupying either entirety, amajority or a significant portion of the front side space and thefingerprint sensing function is provided on the device screen, e.g., oneor more sensing areas for receiving a finger on the device screen. As anexample, FIG. 2A shows a fingerprint sensing zone in the device screenfor a finger to touch which may be illuminated as a visibly identifiablezone or area for a user to place a finger for fingerprint sensing. Sucha fingerprint sensing zone can function like the rest of the devicescreen for displaying images. As illustrated, the device housing of thedevice 200 may have, in various implementations, side facets thatsupport side control buttons that are common in various smartphones onthe market today. Also, one or more optional sensors may be provided onthe front side of the device 200 outside the device screen asillustrated by one example on the left upper corner of the devicehousing in FIG. 2A.

FIG. 2B shows an example of the structural construction of the modulesin the device 200 relevant to the optical fingerprint sensing disclosedin this document. The device screen assembly shown in FIG. 2B includes,e.g., the touch sensing screen module with touch sensing layers on thetop, and a display screen module with display layers located underneaththe touch sensing screen module. An optical sensor module is coupled to,and located underneath, the display screen assembly module to receiveand capture the returned light from the top surface of the touch sensingscreen module and to guide and image the returned light onto an opticalsensor array of optical sensing pixels or photodetectors which convertthe optical image in the returned light into pixel signals for furtherprocessing. Underneath the optical sensor module is the deviceelectronics structure containing certain electronic circuits for theoptical sensor module and other parts in the device 200. The deviceelectronics may be arranged inside the device housing and may include apart that is under the optical sensor module as shown in FIG. 2B.

In implementations, the top surface of the device screen assembly can bea surface of an optically transparent layer serving as a user touchsensing surface to provide multiple functions, such as (1) a displayoutput surface through which the light carrying the display imagespasses through to reach a viewer's eyes, (2) a touch sensing interfaceto receive a user's touches for the touch sensing operations by thetouch sensing screen module, and (3) an optical interface for on-screenfingerprint sensing (and possibly one or more other optical sensingfunctions). This optically transparent layer can be a rigid layer suchas a glass or crystal layer or a flexible layer.

One example of a display screen having light emitting display pixelswithout using backlight is an OLED display having an array of individualemitting pixels, and a thin film transistor (TFT) structure or substratewhich may include arrays of small holes and may be optically transparentand a cover substrate to protect the OLED pixels. Referring to FIG. 2B,the optical sensor module in this example is placed under the OLEDdisplay panel to capture the returned light from the top touch sensingsurface and to acquire high resolution images of fingerprint patternswhen user's finger is in touch with a sensing area on the top surface.In other implementations, the disclosed under-screen optical sensormodule for fingerprint sensing may be implemented on a device withoutthe touch sensing feature. In addition, a suitable display panel may bein various screen designs different from OLED displays.

FIGS. 2C and 2D illustrate an example of a device that implements theoptical sensor module in FIGS. 2A and 2B. FIG. 2C shows a crosssectional view of a portion of the device containing the under-screenoptical sensor module. FIG. 2D shows, on the left, a view of the frontside of the device with the touch sensing display indicating afingerprint sensing area on the lower part of the display screen, and onthe right, a perspective view of a part of the device containing theoptical sensor module that is under the device display screen assembly.FIG. 2D also shows an example of the layout of the flexible tape withcircuit elements.

In the design examples in FIGS. 2A, 2B, 2C and 2D, the opticalfingerprint sensor design is different from some other fingerprintsensor designs using a separate fingerprint sensor structure from thedisplay screen with a physical demarcation between the display screenand the fingerprint sensor (e.g., a button like structure in an openingof the top glass cover in some mobile phone designs) on the surface ofthe mobile device. In the illustrated designs here, the opticalfingerprint sensor for detecting fingerprint sensing and other opticalsignals are located under the top cover glass or layer (e.g., FIG. 2C)so that the top surface of the cover glass serves as the top surface ofthe mobile device as a contiguous and uniform glass surface across boththe display screen layers and the optical detector sensor that arevertically stacked and vertically overlap. This design for integratingoptical fingerprint sensing and the touch sensitive display screen undera common and uniform surface provides benefits, including improveddevice integration, enhanced device packaging, enhanced deviceresistance to exterior elements, failure and wear and tear, and enhanceduser experience over the ownership period of the device.

Various OLED display designs and touch sensing designs can be used forthe device screen assembly above the optical sensor module in FIGS. 2A,2B, 2C and 2D. FIG. 3 illustrates one example of an OLED display andtouch sensing assembly, which is FIG. 7B of U.S. Patent Publication No.US 2015/0331508 A1 published on Nov. 19, 2015, a patent applicationentitled “Integrated Silicon-OLED Display and Touch Sensor Panel” byApple, Inc., which is incorporated by reference as part of thedisclosure of this patent document. OLEDs can be implemented in varioustypes or configurations, including, but not limited to, passive-matrixOLEDs (PMOLEDs), active-matrix OLEDs (AMOLEDs), transparent OLEDs,cathode-common OLEDs, anode-common OLEDs, White OLEDs (WOLEDs), andRGB-OLEDs. The different types of OLEDs can have different uses,configurations, and advantages. In the example of a system having anintegrated Silicon-OLED display and touch sensor panel, the system caninclude a Silicon substrate, an array of transistors, one or moremetallization layers, one or more vias, an OLED stack, color filters,touch sensors, and additional components and circuitry. Additionalcomponents and circuitry can include an electrostatic discharge device,a light shielding, a switching matrix, one or more photodiodes, anear-infrared detector and near-infrared color filters. The integratedSilicon-OLED display and touch sensor panel can be further configuredfor near-field imaging, optically-assisted touch, and fingerprintdetection. In some examples, a plurality of touch sensors and/or displaypixels can be grouped into clusters, and the clusters can be coupled toa switching matrix for dynamic change of touch and/or displaygranularity. In the OLED example in FIG. 3 and other implementations,touch sensors and touch sensing circuitry can include, for example,touch signal lines, such as drive lines and sense lines, groundingregions, and other circuitry. One way to reduce the size of anintegrated touch screen can be to include multi-function circuitelements that can form part of the display circuitry designed to operateas circuitry of the display system to generate an image on the display.The multi-function circuit elements can also form part of the touchsensing circuitry of a touch sensing system that can sense one or moretouches on or near the display. The multi-function circuit elements canbe, for example, capacitors in display pixels of an LCD that can beconfigured to operate as storage capacitors/electrodes, commonelectrodes, conductive wires/pathways, etc., of the display circuitry inthe display system, and that can also be configured to operate ascircuit elements of the touch sensing circuitry. The OLED displayexample in FIG. 3 can be implemented to include multi-touchfunctionality to an OLED display without the need of a separatemulti-touch panel or layer overlaying the OLED display. The OLEDdisplay, display circuitry, touch sensors, and touch circuitry can beformed on a Silicon substrate. By fabricating the integrated OLEDdisplay and touch sensor panel on a Silicon substrate, extremely highpixels per inch (PPI) can be achieved. Other arrangements different fromFIG. 3 for the OLED and touch sensing structures are also possible. Forexample, the touch sensing layers can be an assembly that is located ontop of the OLED display assembly.

Referring back to FIGS. 2A and 2B, the illustrated under-screen opticalsensor module for on-screen fingerprint sensing may be implemented invarious configurations.

In one implementation, a device based on the above design can bestructured to include a device screen a that provides touch sensingoperations and includes a display panel structure having light emittingdisplay pixels each operable to emit light for forming a display image,a top transparent layer formed over the device screen as an interfacefor being touched by a user for the touch sensing operations and fortransmitting the light from the display structure to display images to auser, and an optical sensor module located below the display panelstructure to receive light that is emitted by at least a portion of thelight emitting display pixels of the display structure and is returnedfrom the top transparent layer to detect a fingerprint.

This device can be further configured with various features.

For example, a device electronic control module can be included in thedevice to grant a user's access to the device if a detected fingerprintmatches a fingerprint an authorized user. In addition, the opticalsensor module is configured to, in addition to detecting fingerprints,also detect a biometric parameter different form a fingerprint byoptical sensing to indicate whether a touch at the top transparent layerassociated with a detected fingerprint is from a live person, and thedevice electronic control module is configured to grant a user's accessto the device if both (1) a detected fingerprint matches a fingerprintan authorized user and (2) the detected biometric parameter indicatesthe detected fingerprint is from a live person. The biometric parametercan include, e.g., whether the finger contains a blood flow, or aheartbeat of a person.

For example, the device can include a device electronic control modulecoupled to the display panel structure to supply power to the lightemitting display pixels and to control image display by the displaypanel structure, and, in a fingerprint sensing operation, the deviceelectronic control module operates to turn off the light emittingdisplay pixels in one frame to and turn on the light emitting displaypixels in a next frame to allow the optical sensor array to capture twofingerprint images with and without the illumination by the lightemitting display pixels to reduce background light in fingerprintsensing.

For another example, a device electronic control module may be coupledto the display panel structure to supply power to the light emittingdisplay pixels and to turn off power to the light emitting displaypixels in a sleep mode, and the device electronic control module may beconfigured to wake up the display panel structure from the sleep modewhen the optical sensor module detects the presence of a person's skinat the designated fingerprint sensing region of the top transparentlayer. More specifically, in some implementations, the device electroniccontrol module can be configured to operate one or more selected lightemitting display pixels to intermittently emit light, while turning offpower to other light emitting display pixels, when the display panelstructure is in the sleep mode, to direct the intermittently emittedlight to the designated fingerprint sensing region of the toptransparent layer for monitoring whether there is a person's skin incontact with the designated fingerprint sensing region for waking up thedevice from the sleep mode. Also, the display panel structure may bedesigned to include one or more LED lights in addition to the lightemitting display pixels, and the device electronic control module may beconfigured to operate the one or more LED lights to intermittently emitlight, while turning off power to light emitting display pixels when thedisplay panel structure is in the sleep mode, to direct theintermittently emitted light to the designated fingerprint sensingregion of the top transparent layer for monitoring whether there is aperson's skin in contact with the designated fingerprint sensing regionfor waking up the device from the sleep mode.

For another example, the device can include a device electronic controlmodule coupled to the optical sensor module to receive information onmultiple detected fingerprints obtained from sensing a touch of a fingerand the device electronic control module is operated to measure a changein the multiple detected fingerprints and determines a touch force thatcauses the measured change. For instance, the change may include achange in the fingerprint image due to the touch force, a change in thetouch area due to the touch force, or a change in spacing of fingerprintridges.

For another example, the top transparent layer can include a designatedfingerprint sensing region for a user to touch with a finger forfingerprint sensing and the optical sensor module below the displaypanel structure can include a transparent block in contact with thedisplay panel substrate to receive light that is emitted from thedisplay panel structure and returned from the top transparent layer, anoptical sensor array that receives the light and an optical imagingmodule that images the received light in the transparent block onto theoptical sensor array. The optical sensor module can be positionedrelative to the designated fingerprint sensing region and structured toselectively receive returned light via total internal reflection at thetop surface of the top transparent layer when in contact with a person'sskin while not receiving the returned light from the designatedfingerprint sensing region in absence of a contact by a person's skin.

For yet another example, the optical sensor module can be structured toinclude an optical wedge located below the display panel structure tomodify a total reflection condition on a bottom surface of the displaypanel structure that interfaces with the optical wedge to permitextraction of light out of the display panel structure through thebottom surface, an optical sensor array that receives the light from theoptical wedge extracted from the display panel structure, and an opticalimaging module located between the optical wedge and the optical sensorarray to image the light from the optical wedge onto the optical sensorarray.

Specific examples of under-screen optical sensor modules for on-screenfingerprint sensing are provided below.

FIG. 4A and FIG. 4B show an example of one implementation of an opticalsensor module under the display screen assembly for implementing thedesign in FIGS. 2A and 2B. The device in FIGS. 4A-4B includes a displayassembly 423 with a top transparent layer 431 formed over the devicescreen assembly 423 as an interface for being touched by a user for thetouch sensing operations and for transmitting the light from the displaystructure to display images to a user. This top transparent layer 431can be a cover glass or a crystal material in some implementations. Thedevice screen assembly 423 can include an OLED display module 433 underthe top transparent layer 431. The OLED display module 433 includes,among others, OLED layers including an array of OLED pixels that emitlight for displaying images. The OLED layers have electrodes and wiringstructure optically acting as an array of holes and light scatteringobjects. The array of holes in the OLED layers allows transmission oflight from the top transparent layer 431 through the OLED layers toreach the optical sensor module under the OLED layers and the lightscattering caused by the OLED layers affects the optical detection bythe under-screen optical sensor module for fingerprint sensing. A devicecircuit module 435 may be provided under the OLED display panel tocontrol operations of the device and perform functions for the user tooperate the device.

The optical sensor module in this particular implementation example isplaced under OLED display module 433. The OLED pixels in a fingerprintillumination zone 613 can be controlled to emit light to illuminate thefingerprint sensing zone 615 on the top transparent layer 431 within thedevice screen area for a user to place a finger therein for fingerprintidentification. As illustrated, a finger 445 is placed in theilluminated fingerprint sensing zone 615 as the effective sensing zonefor fingerprint sensing. A portion of the reflected or scattered lightin the zone 615 illuminated by the OLED pixels in the fingerprintillumination zone 613 is directed into the optical sensor moduleunderneath the OLED display module 433 and a photodetector sensing arrayinside the optical sensor module receives such light and captures thefingerprint pattern information carried by the received light.

In this design of using the OLED pixels in the fingerprint illuminationzone 613 within the OLED display panel to provide the illumination lightfor optical fingerprint sensing, the OLED pixels in the fingerprintillumination zone 613 can be controlled to turn on intermittently with arelatively low cycle to reduce the optical power used for the opticalsensing operations. For example, while the rest of the OLED pixels inthe OLED panel are turned off (e.g., in a sleep mode), the OLED pixelsin the fingerprint illumination zone 613 can be turned on intermittentlyto emit illumination light for optical sensing operations, includingperforming optical fingerprint sensing and waking up the OLED panel. Thefingerprint sensing operation can be implemented in a 2-step process insome implementations: first, a few of the OLED pixels in the fingerprintillumination zone 613 within the OLED display panel are turned on in aflashing mode without turning on other OLED pixels in the fingerprintillumination zone 613 to use the flashing light to sense whether afinger touches the sensing zone 615 and, once a touch in the zone 615 isdetected, the OLED pixels in the fingerprint illumination zone 613 areturned on to activate the optical sensing module to perform thefingerprint sensing. Also, upon activating the optical sensing module toperform the fingerprint sensing, the OLED pixels in the fingerprintillumination zone 613 may be operated at a brightness level to improvethe optical detection performance for fingerprint sensing, e.g., at ahigher brightness level than their bright level in displaying images.

In the example in FIG. 4B, the under-screen optical sensor moduleincludes a transparent block 701 that is coupled to the display panel toreceive the returned light from the top surface of the device assemblythat is initially emitted by the OLED pixels in the fingerprint sensingzone 613, and an optical imaging block 702 that performs the opticalimaging and imaging capturing. Light from OLED pixels in the fingerprintillumination zone 613, after reaching the cover top surface, e.g., thecover top surface at the sensing area 615 where a user finger touches,is reflected or scattered back from the cover top surface. Whenfingerprint ridges in close contact of the cover top surface in thesensing area 615, the light reflection under the fingerprint ridges isdifferent, due to the presence of the skin or tissue of the finger incontact at that location, from the light reflection at another locationunder the fingerprint valley, where the skin or tissue of the finger isabsent. This difference in light reflection conditions at the locationsof the ridges and valleys in the touched finger area on the cover topsurface forms an image representing an image or spatial distribution ofthe ridges and valleys of the touched section of the finger. Thereflection light is directed back towards the OLED pixels, and, afterpassing through the small holes of the OLED display module 433, reachesthe interface with the low index optically transparent block 701 of theoptical sensor module. The low index optically transparent block 701 isconstructed to have a refractive index less than a refractive index ofthe OLED display panel so that the returned light can be extracted outof the OLED display panel into the optically transparent block 701. Oncethe returned light is received inside the optically transparent block701, such received light enters the optical imaging unit as part of theimaging sensing block 702 and is imaged onto the photodetector sensingarray or optical sensing array inside the block 702. The lightreflection differences between fingerprint ridges and valleys create thecontrast of the fingerprint image. As shown in FIG. 4B is a controlcircuit 704 (e.g., a microcontroller or MCU) which is coupled to theimaging sensing block 702 and to other circuitry such as the device mainprocessor 705 on a main circuit board.

In this particular example, the optical light path design is such thelight ray enters the cover top surface within the total reflect angleson the top surface between the substrate and air interface will getcollected most effectively by the imaging optics and imaging sensorarray in the block 702. In this design the image of the fingerprintridge/valley area exhibits a maximum contrast. Such an imaging systemmay have undesired optical distortions that would adversely affect thefingerprint sensing. Accordingly, the acquired image may be furthercorrected by a distortion correction during the imaging reconstructionin processing the output signals of the optical sensor array in theblock 702 based on the optical distortion profile along the light pathsof the returned light at the optical sensor array. The distortioncorrection coefficients can be generated by images captured at eachphotodetector pixel by scanning a test image pattern one line pixel at atime, through the whole sensing area in both X direction lines and Ydirection lines. This correction process can also use images from tuningeach individual pixel on one at a time, and scanning through the wholeimage area of the photodetector array. This correction coefficients onlyneed to be generated one time after assembly of the sensor.

The background light from environment (e.g., sun light or room light)may enter the image sensor through OLED panel top surface, through TFTsubstrate holes in the OLED display assembly 433. Such background lightcan create a background baseline in the interested images from fingersand is undesirable. Different methods can be used to reduce thisbaseline intensity. One example is to tune on and off the OLED pixels inthe fingerprint illumination zone 613 at a certain frequency F and theimage sensor accordingly acquires the received images at the samefrequency by phase synchronizing the pixel driving pulse and imagesensor frame. Under this operation, only one of the image phases has thelights emitted from pixels. By subtracting even and odd frames, it ispossible to obtain an image which most consists of light emitted fromthe modulated OLED pixels in the fingerprint illumination zone 613.Based on this design, each display scan frame generates a frame offingerprint signals. If two sequential frames of signals by turning onthe OLED pixels in the fingerprint illumination zone 613 in one frameand off in the other frame are subtracted, the ambient background lightinfluence can be minimized or substantially eliminated. Inimplementations, the fingerprint sensing frame rate can be one half ofthe display frame rate.

A portion of the light from the OLED pixels in the fingerprintillumination zone 613 may also go through the cover top surface, andenter the finger tissues. This part of light power is scattered aroundand a part of this scattered light may go through the small holes on theOLED panel substrate, and is eventually collected by the imaging sensorarray in the optical sensor module. The light intensity of thisscattered light depends on the finger's skin color, the bloodconcentration in the finger tissue and this information carried by thisscattered light on the finger is useful for fingerprint sensing and canbe detected as part of the fingerprint sensing operation. For example,by integrating the intensity of a region of user's finger image, it ispossible to observe the blood concentration increase/decrease depends onthe phase of the user's heart-beat. This signature can be used todetermine the user's heart beat rate, to determine if the user's fingeris a live finger, or to provide a spoof device with a fabricatedfingerprint pattern.

Referring to the OLED display example in FIG. 3, an OLED display usuallyhas different color pixels, e.g., adjacent red, green and blue pixelsform one color OLED pixels. By controlling which color of pixels withineach color pixel to turn on and recording corresponding measuredintensity, the user's skin color may be determined. As an example, whena user registers a finger for fingerprint authentication operation, theoptical fingerprint sensor also measures intensity of the scatter lightfrom finger at color A, and B, as intensity Ia, Ib. The ratio of Ia/Ibcould be recorded to compare with later measurement when user's fingeris placed on the sensing area to measure fingerprint. This method canhelp reject the spoof device which may not match user's skin color.

In some implementations, to provide a fingerprint sensing operationusing the above described optical sensor module when the OLED displaypanel is not turn on, one or more extra LED light sources 703 designatedfor providing fingerprint sensing illumination can be placed on the sideof the transparent block 701 as shown in FIG. 4B. This designated LEDlight 703 can be controlled by the same electronics 704 (e.g., MCU) forcontrolling the image sensor array in the block 702. The designated LEDlight 703 can be pulsed for a short time, at a low duty cycle, to emitlight intermittently and to provide pulse light for image sensing. Theimage sensor array can be operated to monitor the light patternreflected off the OLED panel cover substrate at the same pulse dutycycle. If there is a human finger touching the sensing area 615 on thescreen, the image that is captured at the imaging sensing array in theblock 702 can be used to detect the touching event. The controlelectronics or MCU 704 connected to the image sensor array in the block702 can be operated to determine if the touch is by a human fingertouch. If it is confirmed that it is a human finger touch event, the MCU704 can be operated to wake up the smartphone system, turn on the OLEDdisplay panel (or at least the off the OLED pixels in the fingerprintillumination zone 613 for performing the optical fingerprint sensing),and use the normal mode to acquire a full fingerprint image. The imagesensor array in the block 702 will send the acquired fingerprint imageto the smartphone main processor 705 which can be operated to match thecaptured fingerprint image to the registered fingerprint database. Ifthere is a match, the smartphone will unlock the phone, and start thenormal operation. If the captured image is not matched, the smartphonewill feedback to user that the authentication is failed. User may tryagain, or input passcode.

In the example in FIG. 4 (specifically, FIG. 4B), the under-screenoptical sensor module uses the optically transparent block 701 and theimaging sensing block 702 with the photodetector sensing array tooptically image the fingerprint pattern of a touching finger in contactwith the top surface of the display screen onto the photodetectorsensing array. The optical imaging axis or detection axis 625 from thesensing zone 615 to the photodetector array in the block 702 isillustrated in FIG. 4B. The optically transparent block 701 and thefront end of the imaging sensing block 702 before the photodetectorsensing array forma a bulk imaging module to achieve proper imaging forthe optical fingerprint sensing. Due to the optical distortions in thisimaging process, a distortion correction can be used, as explainedabove, to achieve the desired imaging operation.

In the optical sensing by the under-screen optical sensor module inFIGS. 4A-4B and other designs disclosed herein, the optical signal fromthe sensing zone 615 on the top transparent layer 431 to theunder-screen optical sensor module include different light components.FIGS. 5A and 5B illustrate signal generation for the returned light fromthe sensing zone 615 under two different optical conditions tofacilitate the understanding of the operation of the under-screenoptical sensor module.

FIG. 5A shows how OLED-emitted light from the OLED display module 433,after transmitting through the top transparent layer 431, generatesdifferent returned light signals including light signals that carryfingerprint pattern information to the under-screen optical sensormodule. Two OLED pixels 71 and 73 at two different locations are shownto emit OLED output light beams 80 and 82 that are directed to the toptransparent layer 431 without experiencing total reflection at theinterfaces of the top transparent layer 431. A finger 60 is in contactwith the sensing zone 615 on the e top transparent layer 431. Asillustrated, the OLED light beam 80 reaches to a finger ridge in contactwith the top transparent layer 431 after transmitting through the toptransparent layer 431 to generate the light beam 183 in the fingertissue and another light beam 181 back towards the OLED display module433. The OLED light beam 82 reaches to a finger valley located above thetop transparent layer 431 after transmitting through the top transparentlayer 431 to generate the reflected light beam 185 from the interfacewith the top transparent layer 431 back towards the OLED display module433, a second light beam 189 that enters the finger tissue and a thirdlight beam 187 reflected by the finger valley.

In the example in FIG. 5A, it is assumed that the finger skin'sequivalent index of refraction is about 1.44 at 550 nm and the coverglass index of refraction is about 1.51 for the top transparent layer431. Under those assumptions, the display OLED pixel 71 is turned on atthe finger skin ridge location 61 to produce the beam 80. The fingerridge-cover glass interface reflects part of the beam 80 as reflectedlight 181 to bottom layers 524 below the OLED display module 433. Thereflectance is low, about 0.1%. The majority of the light beam 80becomes the beam 183 that transmits into the finger tissue 60 whichcauses scattering of the light 183 to produce the returned scatteredlight 191 towards the OLED display module 433 and the bottom layers 524.The scattering of the transmitted light beam 189 from the OLED pixel 73in the finger tissue also contributes to the returned scattered light191.

The beam 82 from the display OLED group 73 at the finger skin valleylocation 63, the cover glass surface reflects about 3.5% of the incidentlight 82 power (light 185) to bottom layers 524, and the finger valleysurface reflects about 3.3% of the incident light power (light 187) tobottom layers 524. The total reflection is about 6.8%. The majoritylight 189 is transmitted into the finger tissues 60. Part of the lightpower in the transmitted light 189 in the figure tissue is scattered bythe tissue to contribute to the scattered light 191 towards and into thebottom layers 524.

Therefore, the light reflections from various interface or surfaces atfinger valleys and finger ridges of a touching finger are different andthe reflection ratio difference carries the fingerprint map informationand can be measured to extract the fingerprint pattern of the portionthat is in contact with the top transparent layer 431 and is illuminatedthe OLED light.

FIG. 5B shows how OLED-emitted light from the OLED display module 433,under a total reflection condition at the interface with the toptransparent layer 431, generates different returned light signalsincluding light signals that carry fingerprint pattern information tothe under-screen optical sensor module. It is assumed that the coverglass 431 and the OLED display module 433 are glued together without anyair gap in between so that an OLED light beam emitted by an OLED pixel73 with a large incident angle to the cover glass 431 will be totallyreflected at the cover glass-air interface. When the display OLED pixel73 is turned on, the divergent light beams can be divided into threegroups: (1) central beams 82 with small incident angles to the coverglass 431 without the total reflection, (2) high contrast beams 201,202, 211, 212 that are totally reflected at the cover glass 431 whennothing touches the cover glass surface and can be coupled into fingertissues when a finger touches the cover glass 431, and (3) escapingbeams having very large incident angles that are totally reflected atthe cover glass 431 even at a location where the finger issue is incontact.

For the central light beams 82, the cover glass surface reflects about0.1%-3.5% to light beam 185 that is transmitted into bottom layers 524,the finger skin reflects about 0.1%˜3.3% to light beam 187 that is alsotransmitted into bottom layers 524. The reflection difference isdependent on whether the light beams 82 meet with finger skin ridge 61or valley 63. The rest light beam 189 is coupled into the finger tissues60.

For high contrast light beams 201 and 202, the cover glass surfacereflects nearly 100% to light beams 205 and 206 respectively if nothingtouches the cover glass surface. When the finger skin ridges touch thecover glass surface and at light beams 201 and 202 positions, most ofthe light power is coupled into the finger tissues 60 by light beams 203and 204.

For high contrast light beams 211 and 212, the cover glass surfacereflects nearly 100% to light beams 213 and 214 respectively if nothingtouches the cover glass surface. When the finger touches the cover glasssurface and the finger skin valleys happen to be at light beams 211 and212 positions, no light power is coupled into finger tissues 60.

Similar to the situation in FIG. 5A, light beams that are coupled intofinger tissues 60 will experience random scattering by the figuretissues to form low-contrast light 191.

Therefore, in high contrast light beams illuminated area, finger skinridges and valleys cause different optical reflections and thereflection difference pattern carries the fingerprint patterninformation. The high contrast fingerprint signals can be achieved bycomparing the difference.

The disclosed under-screen optical sensing technology can be in variousconfigurations to optically capture fingerprints based on the design inFIGS. 2A and 2B.

For example, the specific implementation in FIG. 4B based on opticalimaging by using a bulk imaging module in the optical sensing module canbe implemented in various configurations. FIGS. 6A-6C, 7, 8A-8B, 9,10A-10B, 11 and 12 illustrate examples of various implementations andadditional features and operations of the under-screen optical sensormodule designs for optical fingerprint sensing.

FIG. 6A, FIG. 6B and FIG. 6C show an example of an under-screen opticalsensor module based on optical imaging via a lens for capturing afingerprint from a finger 445 pressing on the display cover glass 423.FIG. 6C is an enlarged view of the optical sensor module part shown inFIG. 6B. The under-screen optical sensor module as shown in FIG. 6B isplaced under the OLED display module 433 includes an opticallytransparent spacer 617 that is engaged to the bottom surface of the OLEDdisplay module 433 to receive the returned light from the sensing zone615 on the top surface of the top transparent layer 431, an imaging lens621 that is located between and spacer 617 and the photodetector array623 to image the received returned light from the sensing zone 615 ontothe photodetector array 623. Like the imaging system in the example inFIG. 4B, this imaging system in FIG. 6B for the optical sensor modulecan experience image distortions and a suitable optical correctioncalibration can be used to reduce such distortions, e.g., the distortioncorrection methods described for the system in FIG. 4B.

Similar to the assumptions in FIGS. 5A and 5B, it is assumed that thefinger skin's equivalent index of refraction to be about 1.44 at 550 nmand a bare cover glass index of refraction to be about 1.51 for thecover glass 423. When the OLED display module 433 is glued onto thecover glass 431 without any air gap, the total inner reflection happensin large angles at or larger than the critical incident angle for theinterface. The total reflection incident angle is about 41.8° if nothingis in contact with the cover glass top surface, and the total reflectionangle is about 73.7° if the finger skin touches the cover glass topsurface. The corresponding total reflection angle difference is about31.9°.

In this design, the micro lens 621 and the photodiode array 623 define aviewing angle θ for capturing the image of a contact finger in thesensing zone 615. This viewing angle can be aligned properly bycontrolling the physical parameters or configurations in order to detecta desired part of the cover glass surface in the sensing zone 615. Forexample, the viewing angle may be aligned to detect the total innerreflection of the OLED display assembly. Specifically, the viewing angleθ is aligned to sense the effective sensing zone 615 on the cover glasssurface. The effective sensing cover glass surface 615 may be viewed asa mirror so that the photodetector array effectively detects an image ofa viewing zone or the fingerprint illumination zone 613 in the OLEDdisplay that is projected by the sensing cover glass surface 615 ontothe photodetector array. If the OLED pixels in the viewingzone/fingerprint illumination zone 613 are turned on to emit light, thephotodiode/photodetector array 623 can receives the image of the zone613 that is reflected by the sensing cover glass surface 615. When afinger touches the sensing zone 615, some of the light can be coupledinto the fingerprint's ridges and this will cause the photodetectorarray to receive light from the location of the ridges to appear as adarker image of the fingerprint. Because the geometrics of the opticaldetection path are known, the fingerprint image distortion caused in theoptical path in the optical sensor module can be corrected.

Consider, as a specific example, that the distance H in FIG. 6B from thedetection module central axis to the cover glass top surface is 2 mm.This design can directly cover 5 mm of an effective sensing zone 615with a width Wc on the cover glass. Adjusting the spacer 617 thicknesscan adjust the detector position parameter H, and the effective sensingzone width Wc can be optimized. Because H includes the thickness of thecover glass 431 and the display module 433, the application designshould take these layers into account. The spacer 617, the micro lens621, and the photodiode array 623 can be integrated under the colorcoating 619 on the bottom surface of the top transparent layer 431.

FIG. 7 shows an example of further design considerations of the opticalimaging design for the optical sensor module shown in FIGS. 6A-6C byusing a special spacer 618 to replace the spacer 617 in FIGS. 6B-6C toincrease the size of the sensing area 615. The spacer 618 is designedwith a width Ws and thickness is Hs to have a low refraction index (RI)ns, and is placed under the OLED display module 433, e.g., beingattached (e.g., glued) to the bottom surface the OLED display module433. The end facet of the spacer 618 is an angled or slanted facet thatinterfaces with the micro lens 621. This relative position of the spacerand the lens is different from FIGS. 6B-6C where the lens is placedunderneath the spacer 617. The micro lens 621 and a photodiode array 623are assembled into the optical detection module with a detection anglewidth θ. The detection axis 625 is bent due to optical refraction at theinterface between the spacer 618 and display module 433 and at theinterface between the cover glass 431 and the air. The local incidentangle ϕ1 and ϕ2 are decided by the refractive indices RIs, ns, nc, andna of the materials for the components.

If nc is greater than ns, ϕ1 is greater than ϕ2. Thus, the refractionenlarges the sensing width Wc. For example, assuming the finger skin'sequivalent RI is about 1.44 at 550 nm and the cover glass index RI isabout 1.51, the total reflection incident angle is estimated to be about41.8° if nothing touches the cover glass top surface, and the totalreflection angle is about 73.7° if the finger skin touches the coverglass top surface. The corresponding total reflection angle differenceis about 31.9°. If the spacer 618 is made of same material of the coverglass, and the distance from the detection module center to the coverglass top surface is 2 mm, if detection angle width is 0=31.9°, theeffective sensing area width Wc is about 5 mm. The corresponding centralaxis's local incident angle is ϕ1=ϕ2=57.75°. If the material for thespecial spacer 618 has a refractive index ns about 1.4, and Hs is 1.2 mmand the detection module is tilted at ϕ1=70°. The effective sensing areawidth is increased to be greater than 6.5 mm. Under those parameters,the detection angle width in the cover glass is reduced to 19°.Therefore, the imaging system for the optical sensor module can bedesigned to desirably enlarge the size of the sensing area 615 on thetop transparent layer 431.

When the RI of the special spacer 618 is designed to be sufficiently low(e.g., to use MgF2, CaF2, or even air to form the spacer), the width Wcof the effective sensing area 615 is no longer limited by the thicknessof the cover glass 431 and the display module 433. This property leavesdesigner desired flexibility. In principle, if the detection module hasenough resolution, the effective sensing area can even be increased tocover all the display screen.

Since the disclosed optical sensor technology can be used to provide alarge sensing area for capturing a pattern, the disclosed under-screenoptical sensor modules may be used to capture and detect not only apattern of a finger but a larger size patter such a person's palm thatis associated with a person for user authentication.

FIGS. 8A-8B show an example of further design considerations of theoptical imaging design for the optical sensor module shown in FIG. 7 bysetting the detection angle θ′ of the photodetector array relative inthe display screen surface and the distance L between the lens 621 andthe spacer 618. FIG. 8A shows a cross-sectional view along the directionperpendicular to the display screen surface and FIG. 8B shows a view ofthe device from either the bottom or top of the displace screen. Afilling material 618 c can be used to fill the space between the lens621 and the photodetector array 623. For example, the filling material618 c can be same material of the special spacer 618 or anotherdifferent material. In some designs, the filling material 618 c may theair space.

FIG. 9 shows another example of an under-screen optical sensor modulebased on the design in FIG. 7 where the viewing zone or the fingerprintillumination zone 613 in the OLED display module 433 is designed toinclude one or more extra light sources 614 that are attached to orglued into the same position or region of the viewing zone 613 toprovide additional illumination to the sensing zone 615, thus increasingthe light intensity in optical sensing operations. This is one of waysfor improving the optical sensing sensitivity. The extra light sources614 may be of an expanded type, or be a collimated type so that all thepoints within the effective sensing zone 615 is illuminated. The extralight sources 614 may be a single element light source or an array oflight sources. As mentioned above, the OLED pixels in the viewing zoneor the fingerprint illumination zone 613 in the OLED display module 433may be operated a higher brightness level during the optical fingerprintsensing operation above the brightness level used for displaying imagesin the OLED display.

FIGS. 10A-10B show an example of an under-screen optical sensor modulethat uses an optical coupler 628 shaped as a thin wedge to improve theoptical detection at the optical sensor array 623. FIG. 10A shows across section of the device structure with an under-screen opticalsensor module for fingerprint sensing and FIG. 10B shows a top view ofthe device screen. The optical wedge 628 (with a refractive index n_(s))is located below the display panel structure to modify a totalreflection condition on a bottom surface of the display panel structurethat interfaces with the optical wedge 628 to permit extraction of lightout of the display panel structure through the bottom surface. Theoptical sensor array 623 receives the light from the optical wedge 628extracted from the display panel structure and the optical imagingmodule 621 is located between the optical wedge 628 and the opticalsensor array 623 to image the light from the optical wedge 628 onto theoptical sensor array 623. In the illustrated example, the optical wedge628 includes a slanted optical wedge surface facing the optical imagingmodule and the optical sensing array 623. Also, as shown, there is afree space between the optical wedge 628 and the optical imaging module621.

If the light is totally reflected at the sensing surface of the coverglass 431, the reflectance is 100%, of the highest efficiency. However,the light will also be totally reflected at the OLED bottom surface 433b if it is parallel to the cover glass surfaces. The wedge coupler 628is used to modify the local surface angle so that the light can becoupled out for the detection at the optical sensor array 623. The microholes in the TFT layers of the OLED display module 431 provide thedesired light propagation path for light to transmit through the OLEDdisplay module 431 for the under-screen optical sensing. The actuallight transmission efficiency may gradually be reduced if the lighttransmission angle becomes too large or when the TFT layer becomes toothick. When the angle is close to the total reflection angle, namelyabout 41.8° when the cover glass refractive index is 1.5, thefingerprint image looks good. Accordingly, the wedge angle of the wedgecoupler 628 may be adjusted to be of a couple of degrees so that thedetection efficiency can be increased or optimized. If the cover glass'refractive index is selected to be higher, the total reflection anglebecomes smaller. For example, if the cover glass is made of Sapphirewhich refractive index is about 1.76, the total reflection angle isabout 34.62°. The detection light transmission efficiency in the displayis also improved. Therefore, this design of using a thin wedge to setthe detection angle to be higher than the total reflection angle, and/orto use high refractive index cover glass material to improve thedetection efficiency.

In the under-screen optical sensor module designs in FIGS. 6A-10B, thesensing area 615 on the top transparent surface is not vertical orperpendicular to the detection axis 625 of the optical sensor module sothat the image plane of the sensing area is also not vertical orperpendicular to the detection axis 625. Accordingly, the plane of thephotodetector array 523 can be tilted relative the detection axis 625 toachieve high quality imaging at the photodetector array 623.

FIG. 11 shows three example configurations for this tiling. FIG. 11 (1)shows the sensing area 615 a is tilted and is not perpendicular thedetection axis 625. In a specified case shown in (2), the sensing area615 b is aligned to be on the detection axis 625, its image plane willalso be located on the detection axis 625. In practice, the lens 621 canbe partially cut off so as to simplify the package. In variousimplementations, the micro lens 621 can also be of transmission type orreflection type. For example, a specified approach is illustrated in(3). The sensing area 615 c is imaged by an imaging mirror 621 a. Aphotodiode array 623 b is aligned to detect the signals.

In the above designs where the lens 621 is used, the lens 621 can bedesigned to have an effective aperture that is larger than the apertureof the holes in the OLED display layers that allow transmission of lightthrough the OLED display for optical fingerprint sensing. This designcan reduce the undesired influence of the wiring structures and otherscattering objects in the OLED display module.

In some implementations of the disclosed fingerprint technology, thefingerprint sensing contrast at the optical sensor array 623 can beimproved by controlling the OLED pixels (613) of the display screen thatprovide the illumination for capturing the fingerprint patterns in thefingerprint touch sensing. When the fingerprint sensor is activated,e.g., due to presence of a touch, the OLED pixels in the local viewingzone 613 can be turned on with high brightness to improve thefingerprint sensing contrast. For example, the brightness of the OLEDpixels in the local viewing zone 613 can be controlled to be higher thanits maximum brightness when the same OLED pixels in the local viewingzone 613 are used as a regular display.

The under-screen optical sensing disclosed in this patent document canbe adversely affected by noise from various factors including thebackground light from the environment in which a device is used. Varioustechniques for reducing the background light noise are provided.

For example, the undesired background light in the fingerprint sensingmay be reduced by providing proper optical filtering in the light path.One or more optical filters may be used to reject the environment lightwavelengths, such as near IR and partial of the red light etc. In someimplementation, such optical filter coatings may be made on the surfacesof the optical parts, including the display bottom surface, prismsurfaces, sensor surface etc. For example, human fingers absorb most ofthe energy of the wavelengths under ˜580 nm, if one or more opticalfilters or optical filtering coatings can be designed to reject light inwavelengths from 580 nm to infrared, undesired contributions to theoptical detection in fingerprint sensing from the environment light maybe greatly reduced. More details on background reduction based onoptical filtering are provided in later sections.

FIGS. 12 and 13 show two examples of techniques based on particularlyways of capturing and processing optical signals at the optical sensormodule.

FIG. 12 shows an example of an operation of the fingerprint sensor forreducing or eliminating undesired contributions from the backgroundlight in fingerprint sensing. The optical sensor array can be used tocapture various frames and the captured frames can be used to performdifferential and averaging operations among multiple frames to reducethe influence of the background light. For example, in frame A the OLEDdisplay is turned on to illuminate the finger touching area, in frame Bthe illumination is changed or turned off. Subtraction of the signals offrame B from the signals of frame A can be used in the image processingto reduce the undesired background light influence.

FIG. 13 shows an example of an operation process for correcting theimage distortion in the optical sensor module. At step 1301, certaindisplay pixels are controlled and operated to emit light in a specificregion, and the light emission of such pixels is modulated by afrequency F. Ate step 1302, an imaging sensor under the display panel isoperated to capture the image at a frame rate at the same frequency F.In the optical fingerprint sensing operation, a finger is placed on topof the display panel cover substrate and the presence of the fingermodulates the light reflection intensity of the display panel coversubstrate top surface. The imaging sensor under the display captures thefingerprint modulated reflection light pattern. At step 1303, thedemodulation of the signals from image sensors is synchronized with thefrequency F, and the background subtraction is performed. The resultantimage has a reduced background light effect and includes images frompixel emitting lights. At step 1304, the capture image is processed andcalibrated to correct image system distortions. At step 1305, thecorrected image is used as a human fingerprint image for userauthentication.

The same optical sensors used for capturing the fingerprint of a usercan be used also to capture the scattered light from the illuminatedfinger as shown by the back scattered light 191 in FIGS. 5A and 5B. Thedetector signals from the back scattered light 191 in FIGS. 5A and 5B ina region of interest can be integrated to produce an intensity signal.The intensity variation of this intensity signal is evaluated todetermine the heart rate of the user.

The above fingerprint sensor may be hacked by malicious individuals whocan obtain the authorized user's fingerprint, and copy the stolenfingerprint pattern on a carrier object that resembles a human finger.Such unauthorized fingerprint patterns may be used on the fingerprintsensor to unlock the targeted device. Hence, a fingerprint pattern,although a unique biometric identifier, may not be by itself acompletely reliable or secure identification. The under-screen opticalsensor module can also be used to as an optical anti-spoofing sensor forsensing whether an input object with fingerprint patterns is a fingerfrom a living person and for determining whether a fingerprint input isa fingerprint spoofing attack. This optical anti-spoofing sensingfunction can be provided without using a separate optical sensor. Theoptical anti-spoofing can provide high-speed responses withoutcompromising the overall response speed of the fingerprint sensingoperation.

FIG. 14A shows exemplary optical extinction coefficients of materialsbeing monitored in blood where the optical absorptions are differentbetween the visible spectral range e.g., red light at 660 nm and theinfrared range, e.g., IR light at 940 nm. By using probe light toilluminate a finger at a first visible wavelength (Color A) and a seconddifferent wavelength such as an IR wavelength (Color B), the differencesin the optical absorption of the input object can be captured determinewhether the touched object is a finger from a live person. Since theOLED pixels include OLED pixels emitting light of different colors toemit probe light at least two different optical wavelengths to use thedifferent optical absorption behaviors of the blood for live fingerdetection. When a person' heart beats, the pulse pressure pumps theblood to flow in the arteries, so the extinction ratio of the materialsbeing monitored in the blood changes with the pulse. The received signalcarries the pulse signals. These properties of the blood can be used todetect whether the monitored material is a live-fingerprint or a fakefingerprint.

FIG. 14B shows a comparison between optical signal behaviors in thereflected light from a nonliving material (e.g., a fake finger) and alive finger. The optical fingerprint sensor can also operate as aheartbeat sensor to monitor a living organism. When two or morewavelengths of the probe light are detected, the extinction ratiodifference can be used to quickly determine whether the monitoredmaterial is a living organism, such as live fingerprint. In the exampleshown in FIG. 14B, probe light at different wavelengths were used, oneat a visible wavelength and another at an IR wavelength as illustratedin FIG. 14A.

When a nonliving material touches the top cover glass above thefingerprint sensor module, the received signal reveals strength levelsthat are correlated to the surface pattern of the nonliving material andthe received signal does not contain signal components associated with afinger of a living person. However, when a finger of a living persontouches the top cover glass, the received signal reveals signalcharacteristics associated with a living person, including obviouslydifferent strength levels because the extinction ratios are differentfor different wavelengths. This method does not take long time todetermine whether the touching material is a part of a living person. InFIG. 14B, the pulse-shaped signal reflects multiple touches instead ofblood pulse. Similar multiple touches with a nonliving material does notshow the difference caused by a living finger.

This optical sensing of different optical absorption behaviors of theblood at different optical wavelengths can be performed in a shortperiod for live finger detection and can be faster than opticaldetection of a person's heart beat using the same optical sensor.

FIG. 15 shows an example of an operation process for determining whetheran object in contact with the OLED display screen is part of a finger ofa live person by operating the OLED pixels to illuminate the finger intwo different light colors.

For yet another example, the disclosed optical sensor technology can beused to detect whether the captured or detected pattern of a fingerprintor palm is from a live person's hand by a “live finger” detectionmechanism by other mechanisms other than the above described differentoptical absorptions of blood at different optical wavelengths. Forexample, a live person's finger tends to be moving or stretching due tothe person's natural movement or motion (either intended or unintended)or pulsing when the blood flows through the person's body in connectionwith the heartbeat. In one implementation, the optical sensor module candetect a change in the returned light from a finger or palm due to theheartbeat/blood flow change and thus to detect whether there is a liveheartbeat in the object presented as a finger or palm. The userauthentication can be based on the combination of the both the opticalsensing of the fingerprint/palm pattern and the positive determinationof the presence of a live person to enhance the access control. For yetanother example, as a person touches the OLED display screen, a changein the touching force can be reflected in one or more ways, includingfingerprint pattern deforming, a change in the contacting area betweenthe finger and the screen surface, fingerprint ridge widening, or ablood flow dynamics change. Those and other changes can be measured byoptical sensing based on the disclosed optical sensor technology and canbe used to calculate the touch force. This touch force sensing can beused to add more functions to the optical sensor module beyond thefingerprint sensing.

In the above examples where the fingerprint pattern is captured on theoptical sensor array via an imaging module as in FIG. 4B and FIG. 6B,optical distortions tend to degrade the image sensing fidelity. Suchoptical distortions can be corrected in various ways. FIG. 16 shows anexample of a standard calibration pattern produced by the OLED displayfor calibrating the imaging sensing signals output by the optical sensorarray for fingerprint sensing. The fingerprint sensing module calibratesthe output coordinates referencing on the image of the standard pattern.

In light of the disclosure in this patent document, variousimplementations can be made for the optical sensor module as disclosed.

For example, a display panel can be constructed in which each pixelemitting lights, and can be controlled individually; the display panelincludes an at least partially transparent substrate; and a coversubstrate, which is substantially transparent. An optical sensor moduleis placed under the display panel to sense the images form on the top ofthe display panel surface. The optical sensor module can be used tosense the images form from light emitting from display panel pixels. Theoptical sensor module can include a transparent block with refractiveindex lower than the display panel substrate, and an imaging sensorblock with an imaging sensor array and an optical imaging lens. In someimplementations, the low refractive index block has refractive index inthe range of 1.35 to 1.46 or 1 to 1.35.

For another example, a method can be provided for fingerprint sensing,where light emitting from a display panel is reflected off the coversubstrate, a finger placed on top of the cover substrate interacts withthe light to modulate the light reflection pattern by the fingerprint.An imaging sensing module under the display panel is used to sense thereflected light pattern image and reconstruct fingerprint image. In oneimplementation, the emitting light from the display panel is modulatedin time domain, and the imaging sensor is synchronized with themodulation of the emitting pixels, where a demodulation process willreject most of the background light (light not from pixels beingtargeted).

Various design considerations for the disclosed under-screen opticalsensor module for optical fingerprint sensing are further described inin the International Patent Application No. PCT/US2016/038445 entitled“MULTIFUNCTION FINGERPRINT SENSOR HAVING OPTICAL SENSING CAPABILITY”filed on Jun. 20, 2016 (claiming priority from U.S. Provisional PatentApplication No. 62/181,718, filed on Jun. 18, 2015 and published underInternational Publication No. WO 2016/205832 A1 on Dec. 22, 2016) andInternational Patent Application No. PCT/CN2016/104354 entitled“MULTIFUNCTION FINGERPRINT SENSOR HAVING OPTICAL SENSING AGAINSTFINGERPRINT SPOOFING” filed on Nov. 2, 2016 (claiming priority from U.S.Provisional Patent Application No. 62/249,832, filed on Nov. 2, 2015 andpublished under International Publication No. WO 2017/076292 A1). Theentire disclosures of the above mentioned patent applications areincorporated by reference as part of the disclosure of this patentdocument.

In various implementations of the under-screen optical sensor moduletechnology for fingerprint sensing disclosed herein, the optical imagingof the illuminated touched portion of a finger to the optical sensorarray in the under-screen optical sensor module can be achieved withoutusing an imagine module such as a lens by imaging the returned lightfrom the touched portion of the finger under optical illumination. Onetechnical challenge for optical fingerprint sensing without an imagingmodule is how to control the spreading of the returned light that mayspatially scramble returned light from different locations on thetouched portion of the finger at the optical sensor array so that thespatial information of different locations may be lost when suchreturned light reaches the optical sensor array. This challenge can beaddressed by using optical collimators or an array of pinholes toreplace the optical imaging module in the under-screen optical sensormodule for detecting a fingerprint by optical sensing. A device forimplementing such optical fingerprint sending can include a devicescreen that provides touch sensing operations and includes a displaypanel structure having light emitting display pixels, each pixeloperable to emit light for forming a portion of a display image; a toptransparent layer formed over the device screen as an interface forbeing touched by a user for the touch sensing operations and fortransmitting the light from the display structure to display images to auser; and an optical sensor module located below the display panelstructure to receive light that is emitted by at least a portion of thelight emitting display pixels of the display structure and is returnedfrom the top transparent layer to detect a fingerprint, the opticalsensor module including an optical sensor array that receives thereturned light and an array of optical collimators or pinholes locatedin a path of the returned light to the optical sensor array. The arrayof optical collimators are used to collect the returned light from thedisplay panel structure and to separate light from different locationsin the top transparent layer while directing the collected returnedlight to the optical sensor array.

The imaging by using collimators relies on using different collimatorsat different locations to spatially separate light from differentregions of a fingerprint to different optical detectors in the opticaldetector array. The thickness or length of each collimator along thecollimator can be designed to control the narrow field of optical viewof each collimator, e.g., the light from only a small area on theilluminated finger is captured by each collimator and is projected ontoa few adjacent optical detectors in the optical detector array. As anexample, the thickness or length of each collimator along the collimatorcan be designed to be large, e.g., a few hundred microns, so that thefield of optical view of each collimator may allow the collimator todeliver imaging light to a small area on the optical detector array,e.g., one optical detector or a few adjacent optical detectors in theoptical detector array (e.g., an area of tens of microns on each side onthe optical detector array in some cases).

The following sections explain how an array of optical collimators orpinholes can be used for under-screen optical fingerprint sensing by theexamples for using optical collimators in optical fingerprint sensing inhybrid sensing pixels each having a capacitive sensor for capturingfingerprint information and an optical sensor for capturing fingerprintinformation.

FIGS. 17A and 17B show two examples of hybrid sensing pixel designs thatcombine capacitive sensing and optical sensing within the same sensingpixel.

FIG. 17A shows an example of a fingerprint sensor device 2100 thatincorporates a capacitive sensor in addition to an optical sensor foreach sensor pixel of an array of sensor pixels in capturing fingerprintinformation. By combining both capacitive sensors and optical sensors,fingerprint images obtained with the optical sensors can be used tobetter resolve the 3D fingerprint structure obtained with the capacitivesensors. For illustrative purposes, the structure shown in FIG. 17Arepresents one sensor pixel in an array of sensor pixels and each sensorpixel includes an optical sensor 2102 and a capacitive sensor 2114 thatare disposed next to each other within the same pixel.

The optical sensor 2102 includes a photodetector 2108 and a collimator2106 disposed over the photodetector 2108 to narrow or focus reflectedlight 2124 from finger 2102 toward the photodetector 2108. One or morelight sources, such as LEDs (not shown) can be disposed around thecollimator 2106 to emit light, which is reflected off the finger asreflected light 2124 and is directed or focused toward the correspondingphotodetector 2108 to capture a part of the fingerprint image of thefinger 2102. The collimator 2106 can be implemented using an opticalfiber bundle or one or more metal layer(s) with holes or openings. Thisuse of multiple optical collimators above the optical detector array maybe used as a lensless optical design for capturing the fingerprint imagewith a desired spatial resolution for reliable optical fingerprintssensing. FIG. 17A shows the collimator 2106 implemented using one ormore metal layers 2110 with holes or openings 2112. The collimator 2106in the layer between the top structure or layer 2104 and thephotodetectors 2108 in FIG. 17A includes multiple individual opticalcollimators formed by optical fibers or by holes or openings in one ormore layers (e.g., silicon or metal) and each of such individual opticalcollimators receives light ray 2124 in a direction along thelongitudinal direction of each optical collimator or within a smallangle range that can be captured by the top opening of each opening orhole and by the tubular structure as shown so that light rays incidentin large angles from the longitudinal direction of each opticalcollimator are rejected by each collimator from reaching the opticalphotodiode on the other end of the optical collimator.

In the capacitive sensing part of each sensing pixel, the capacitivesensor 2114 includes a capacitive sensor plate 2116 that iselectromagnetically coupled to a portion of a finger that is eithernearby or in contact with the sensing pixel to perform the capacitivesensing. More specifically, the capacitive sensor plate 2116 and thefinger 2102 interact as two plates of one or more capacitive elements2122 when the finger 2102 is in contact with or substantially near theoptional cover 2104 or a cover on a mobile device that implements thefingerprint sensor device 2100. The number of capacitive sensor plates2116 can vary based on the design of the capacitive sensor 2114. Thecapacitive sensor plate 2116 can be implemented using one or more metallayers. The capacitive sensor plate 2116 is communicatively coupled tocapacitive sensor circuitry 2120 so that the capacitive sensor circuitry2120 can process the signals from the capacitive sensor plate 2116 toobtain data representing the 3D fingerprint structure. A routing orshielding material can be disposed between the capacitive sensor plate2116 and the capacitive sensor circuitry to electrically shield themetal plate 2116. The capacitive sensor circuitry 2120 can becommunicatively coupled to both the capacitive sensor plate 2116 and thephotodetector 2108 to process both the signal from the capacitive sensorplate 2116 and the signal from the photodetector 2108. In FIG. 17A, thecapacitive sensor and the optical sensor within each hybrid sensingpixel are adjacent to and displaced from each other without beingspatially overlapped.

In implementations, the optical sensing features in the hybrid sensordesign in FIG. 17A such as the optical collimator design can be used inan under-screen optical sensor module. Therefore, the optical sensingwith the optical collimator feature in FIG. 17A may be implemented in amobile device or an electronic device is capable of detecting afingerprint by optical sensing to include a display screen structure; atop transparent layer formed over the display screen structure as aninterface for being touched by a user and for transmitting the lightfrom the display screen structure to display images to a user; and anoptical sensor module located below the display screen structure toreceive light that is returned from the top transparent layer to detecta fingerprint. The optical sensor module includes an optical sensorarray of photodetectors that receive the returned light and an array ofoptical collimators to collect the returned light from the toptransparent layer via the display screen structure and to separate lightfrom different locations in the top transparent layer while directingthe collected returned light through the optical collimators to thephotodetectors of the optical sensor array.

FIG. 17B illustrates another example of a fingerprint sensor device 2130that structurally integrates an optical sensor and a capacitive sensorin each hybrid sensor pixel in a spatially overlap configuration in anarray of sensor pixels to reduce the footprint of each hybrid sensingpixel. The fingerprint sensor device 2130 includes a semiconductorsubstrate 2131, such as silicon. Over the substrate 2131, multiplesensing elements or sensing pixels 2139 are disposed. Each sensingelement or sensing pixel 2139 includes active electronics circuitry area2132 including CMOS switches, amplifier, resistors and capacitors forprocessing sensor signals. Each sensing pixel or sensing element 2139includes a photodetector 2133 disposed or embedded in the activeelectronics circuitry area 2132. A capacitive sensor plate or a topelectrode 2134 of the capacitive sensor for capacitive sensing isdisposed over a photodetector 2133 and includes a hole or opening 2138on the sensor plate 2134 to function also as a collimator of light fordirecting light onto the photodetector 2133. A via 2135 filled withconductive material is disposed to electrically connect the topelectrode 2134 to the active circuit elements 2132. By adjusting theopening or the hole and the distance of the top electrode 2134 with thephotodetector 2133, the light collecting angle 2137 of the photodetector(e.g., photodiode) 2133 can be adjusted. The fingerprint sensor device2130 is covered by a protective cover 2136, which includes hardmaterials, such as sapphire, glass etc. Photodetector 2133 lightcollection angle 2137 can be designed to preserve the spatial resolutionof the image collected by the photodiode arrays. A light source 2140,such as an LED, is placed under the cover, on the side of fingerprintsensor device 2130 to emit light, which is reflected off the finger anddirected toward the photodetector 2133 to capture the fingerprint image.When a finger touches or comes substantially near the protective cover,the finger and the sensing top electrode 2134 in combination form acapacitive coupling (e.g., capacitor 2142) between the human body andsensing top electrode 2134. The fingerprint sensor device 2130 thatincludes both optical and capacitive sensors can acquire images of botha light reflection image of fingerprint and also a capacitive couplingimage. The sensing top electrode 2134 serves dual purpose: 1) forcapacitive sensing, and 2) as a collimator (by fabricating one or moreholes on the sensing top electrode 2134) to direct, narrow or focusreflected light from the finger toward the photodetector 2133. Reusingthe sensing top electrode 2134 eliminates the need for additional metallayer or optical fiber bundle, and thus reduces each pixel size andaccordingly the overall size of the fingerprint sensor device 2130.

In FIG. 17B, the optical sensing design uses the holes or openings 2138formed between the top layer 2136 and the bottom array of photodetectors2133 as an optical collimators to select only light rays within certainangles 2137 to preserve the spatial resolution of the image collected bythe photodetectors 2133 in the photodetector array as illustrated.Similar to the fiber or other tubular shaped optical collimators in FIG.17A, the holes or openings 2138 formed between the top layer 2136 andthe bottom array of photodetectors 2133 constitute optical collimatorsto collect the returned light from the top transparent layer via thedisplay screen structure and to separate light from different locationsin the top transparent layer while directing the collected returnedlight through the optical collimators to the photodetectors 2133.

FIG. 18 is a top-down view of an exemplary hybrid fingerprint sensordevice 2200 incorporating both an optical sensor and a capacitive sensorin each hybrid sensing pixel. The fingerprint sensor device 2200 isimplemented as a CMOS silicon chip 2221 that includes an array of hybrid(incorporating both an optical sensor and a capacitive sensor) sensingelements or pixels 2222. Alternatively, the layout in FIGS. 22A-22B canalso be for all optical sensing designs disclosed in this document wherethe openings or holes 2223 represent the optical collimators in FIG. 17Aor 17B. The size or dimension of the sensing elements can be in therange of 25 μm to 250 μm, for example. The hybrid sensor device 2200 caninclude an array of support circuitry including amplifiers, ADCs, andbuffer memory in a side region 2224. In addition, the hybrid sensordevice 2200 can include an area for wire bonding or bump bonding 2225. Atop layer 2226 of the hybrid sensor element 2222 can include a metalelectrode for capacitive sensing. One or more openings or holes 2223 canbe fabricated on each top metal electrode 23 to structurally serve as acollimator for directing light in a vertical direction to shine on aphotodetector under the top electrode. Thus, the top layer 2226structure can serve dual purposes of optical and capacitive sensing. Asensor device processor can be provided to process the pixel outputsignals from hybrid sensing pixels to extract the fingerprintinformation.

In addition to sharing the same structure for capacitive sensing and forfocusing light in the vertical direction as a collimator, one instanceof sensor signal detection circuitry can be shared between the opticaland capacitive sensors to detect the sensor signals from both aphotodetector and a capacitive sensor plate.

FIG. 19A illustrates a circuit diagram for an exemplary hybridfingerprint sensing element or pixel 2300 having both capacitive sensingand optical sensing functions for fingerprints. The exemplary sensorpixel 2300 includes sensor signal detection circuitry 2316 toselectively switch between detecting or acquiring sensor signals from asensing top electrode (e.g., a top metal layer) 2308 based on capacitivesensing and a photodetector (e.g., a photodiode) 2314 based on opticalsensing to acquire both a reflective optical image from thephotodetector 2314 and a capacitive coupled image from the capacitivesensor electrode 2308 from a finger. In some implementations, the twoimages from the two sensing mechanisms in each hybrid sensing pixel canbe serially processed by the sensor signal detection circuitry. In theillustrated example, switches 2310 and 2312 have first terminals thatare electrically coupled to the sensing top electrode 2308 and thephotodetector 2314, respectively, and second terminals that are coupledto a common input terminal of the sensor signal detection circuitry 2316to provide corresponding optical detector signal from the photodetector2314 and the corresponding capacitive sensing signal from the sensingtop electrode 2308 to the sensor signal detection circuitry 2316. Whenthe switch 2310 is turned off (CAP_EN=0) and the switch 2312 is turnedon (Optical_en=1), the sensor signal detection circuitry 2316 acquiresthe optical detector signal representing the optical image of thescanned fingerprint received at the particular hybrid sensing pixel. Thesensor signal detection circuitry 2316 can acquire the capacitivesensing signal representing the capacitive image of the scannedfingerprint when switch 2310 CAP_EN=1 and Optical_en=0. After both theoptical and capacitive images are acquired, both images can be processedin downstream circuitry separately and in combination to identify thefingerprint characteristics.

With the two modality of imaging by the above hybrid sensing pixels, theperformance of the fingerprint identification can be enhanced by makinguse of the two types of the images in different ways. This enhancedfingerprint identification can be achieved by the sensor deviceprocessor, such as sensor device processor 2321, for processing thepixel output signals from the hybrid sensing pixels to extract thefingerprint information. For example, the capacitive image can provide a3D image on the depth of the ridges and valleys of the fingerprintfeatures. Complementing the 3D capacitive image, the optical image canprovide a high resolution 2D information on the fingerprintcharacteristics. The optical 2D image having a higher spatial resolutioncan be used to recover the capacitive sensing image resolution becauseboth images information on the same ridges of the fingerprint. In someimplementations where the capacitive sensing method may be moresensitive and accurate on identifying the valleys of the fingerprintthan the optical sensing method, the spatial resolution of imagesacquired using the capacitive sensing method can degrade based on thethickness of the cover. This aspect of the capacitive sensing can besupplemented by the optical sensing. In operation, the sensor responsemay be fixed and the point spread function of the capacitive sensor maybe fixed for all sensor positions. The higher resolution optical sensingcan be used as a resolution recovery method and can be applied on thecapacitive sensing image to enhance the 3D image. A partial highresolution image from optical sensing can be available to help with therecovering method. Thus, the 3D capacitive image can be enhanced toprovide more information on the valleys and ridges by interpolating orrecovering based on the high resolution 2D image.

The enhanced 3D image can provide an improved fingerprint recognitionand matching. In another example, the optical and capacitive images canbe stored together to provide two comparisons each time a fingerprintrecognition or matching is performed. The use of two types of images forcomparison enhances the accuracy and security of the fingerprint sensingsystem.

The sensor signal detection circuitry 2316 can be implemented in variousways using a number different circuitry designs. In one example,integrator sensing circuitry 2318 can be implemented to store theelectric charges caused by ridges and valleys touching or beingsubstantially near the cover of the fingerprint sensor device of thecover of the mobile device. The inclusion of the integrator circuitry2318 enhances the signal-to-noise ratio (SNR). The integrator sensingcircuitry includes an operational amplifier 2322 to amplify a sensorsignal, such as a capacitance related or optical related signal (e.g.,voltage signal), detected by the sensing top electrode 2308 or thephotodetector 2314 of the exemplary sensor pixel 2300. The sensing topelectrode 2308 that include a conductive material, such as one of avariety of metals is electrically connected to a negative or invertingterminal 2328 of the amplifier 2322 through the switch 2310. The sensingtop electrode 2108 and a local surface of the finger 2302 function asopposing plates of a capacitor Cf 2302. The capacitance of the capacitorCf 2302 varies based on a distance ‘d’ between the local surface of thefinger and the sensing top electrode 2308, the distance between the twoplates of the capacitor Cf 2302. The capacitance of capacitor Cf 2302 isinversely proportional to the distance ‘d’ between the two plates of thecapacitor Cf 2302. The capacitance of capacitor Cf 2302 is larger whenthe sensing top electrode 2308 is opposite a ridge of the finger thanwhen opposite a valley of the finger.

In addition, various parasitic or other capacitors can be formed betweendifferent conductive elements in the exemplary sensor pixel 2300. Forexample, a parasitic capacitor CP 2304 can form between the sensing topelectrode 2308 and a device ground terminal 2305. Device ground iscoupled to earth ground closely. Another capacitor Cr 2324 can formbetween an output conductor of the amplifier 2322 and the negative orinverting terminal 2328 of the amplifier 2322 and functions as afeedback capacitor to the amplifier 2322. Also, a switch 2326 can becoupled between the output of the amplifier 2322 and the negative orinverting terminal 2328 of the amplifier 2322 to reset the integratorcircuitry 2318.

The positive terminal of the amplifier 2322 is electrically connected toan excitation signal Vref. The excitation signal Vref can be directlyprovided to the positive terminal of a dedicated amplifier in eachsensor pixel. By providing the excitation signal Vref directly to thepositive terminal of the amplifier 2322, the exemplary sensor pixel 2100becomes an active sensor pixel. In addition, providing the excitationsignal Vref directly to the positive terminal of the amplifier 2322eliminates the need to include an excitation electrode, common to allsensor pixels, which reduces a conductive (e.g., metal) layer from thesemiconductor structure of the sensor chip. In some implementations, anoptional excitation electrode 2306 can be implemented to enhance the SNRbased on the design of the sensor pixel. In addition, by providing theexcitation signal Vref 2330 directly to the amplifier 2322, theexcitation signal Vref 2322 is not applied directly to the finger toavoid potentially irritating or injuring the finger. Moreover, when theexcitation electrode for applying the excitation signal directly to thefinger is not used, all components of the fingerprint sensor device canbe integrated into a single packaged device, and the entire fingerprintsensor device can be disposed under the protective cover glass. With theentire fingerprint sensor device disposed under the protective coverglass, the fingerprint sensor device is protected from the finger andother external elements that can potentially damage the fingerprintsensor.

In FIG. 19A, the output signal (optical and capacitive) of the sensorsignal detection circuitry 2316 (e.g., Vpo of the amplifiers 2322) inthe sensor pixels 2300 is electrically coupled to a switch 2320 toselectively output the output signal Vpo from the sensor pixel 2300 to asignal processing circuity including a filter. The switch 2320 can beimplemented using a transistor or other switching mechanisms andelectrically coupled to a controller to control the switching of theswitch 2320. By controlling the switches 2320, 2310 and 2312, the sensorpixels in an array of sensor pixels can be selectively switched betweenacquiring the optical signals and the capacitive signals. In oneimplementation, the optical or capacitive signal can be acquired foreach line, row or column of sensor pixels in the array and then switchedto acquire the other type of signal for the line, row or column. Theswitching between the optical and capacitive signal acquisition can beperformed line-by-line. In another implementation, one type of signal(capacitive or optical) can be acquired for all sensor pixels orelements in the array and then switched to acquire the other type ofsignal for all of the sensor pixels or elements. Thus, the switchingbetween acquisition of different signal types can occur for the entirearray. Other variations of switching between acquisition of the twotypes of sensor signals can be implemented.

FIG. 19B illustrates a circuit diagram for another exemplary hybridfingerprint sensing element or pixel 2340. The hybrid fingerprintsensing element or pixel 2340 is substantially the same as the hybridfingerprint sensing element or pixel 2300 with respect to the componentshaving the same reference number. For descriptions of the commoncomponents having the same reference number, refer to the description ofFIG. 19A.

The hybrid fingerprint sensing element or pixel 2340 implements thesensing top electrode 2308 to include a hole or opening 2342 thatfunctions as a collimator to focus or narrow the reflected light 2344toward the photodetector 2314 (e.g., photodiode). The photodetector 2314can be positioned or disposed below the collimator implemented using thesensing top electrode 2308 to capture the reflected light 2344 focusedby the collimator 2308.

In some implementations, separate instances of sensor signal detectioncircuitry can be included for the optical and capacitive sensors todetect in parallel the sensor signals from both a photodetector and acapacitive sensor plate.

FIG. 19C illustrates a circuit diagram of an exemplary hybridfingerprint sensing element or pixel 2350 for performing paralleldetection of sensor signals from the photodetector and the capacitivesensor plate. The hybrid fingerprint sensing element or pixel 2350 issubstantially the same as the hybrid fingerprint sensing element orpixel 2340 with respect to the components having the same referencenumber. For descriptions of the common components having the samereference number, refer to the description of FIG. 19A.

To perform sensor signal detection from both the capacitive plate andthe photodetector in parallel, the hybrid fingerprint sensing element orpixel 2350 includes separate sensor signal detection circuitry 2316 and2317 communicatively coupled to the sensing top electrode 2308 and thephotodetector 2324 respectively. Sensor signal detection circuitry 2317can be implemented to be substantially similar to sensor signaldetection circuitry 2316. In some implementations, switches 2310 and2312 can be disposed to have first terminals that are electricallycoupled to the sensing top electrode 2308 and the photodetector 2314,respectively, and second terminals that are coupled to respective sensorsignal detection circuitry 2316 and 2317 to provide the optical detectorsignal from the photodetector 2314 and the capacitive sensing signalfrom the sensing top electrode 2308 to the sensor signal detectioncircuitry 2316 and 2317 respectively When the switches 2310 and 2312 areturned on and off together, the sensor signal detection circuitry 2316and 2317 can perform sensor signal detection from the capacitive plate2308 and the photodetector 2314 in parallel. When the switches 2310 and2312 are turned on and off out of phase with each other, the sensorsignal detection circuitry 2316 and 2317 can perform sensor signaldetection from the capacitive plate 2308 and the photodetector 2314 inseries. In addition, the sensor device processor 2321 can becommunicatively coupled to the sensor signal detection circuitry 2316and 2317 either directly or indirectly through switches 2320A and 2320Bto process the detected sensor signals from the capacitive plate 2308and the photodetector 2314 in parallel or in series.

In another aspect of the disclosed technology, the optical sensordescribed with respect to FIGS. 17A, 17B, 18, 19A and 19B can be used tomeasure human heart beat by measuring the reflected light intensitychange with time caused by blood flow variations in fingers due to theheart beat and pumping actions of the heart. This information iscontained in the received light that is reflected, scattered or diffusedby the finger and is carried by the optical detector signal. Thus, theoptical sensor can serve multiple functions including acquiring anoptical image of the fingerprint and to measure human heart beat. Inimplementations, a sensor device processor is used to process one ormore optical detector signals to extract the heart beat information.This sensor device processor may be the same sensor device processorthat processes the pixel output signals from optical sensing pixels orhybrid sensing pixels to extract the fingerprint information.

FIGS. 20, 21A-21B, and 22A-22B illustrate examples of various designsfor fingerprint sensing using an under-screen optical sensor moduleusing an array of optical collimators or pinholes for directing signallight carrying fingerprint information to the optical sensor array. Suchoptical collimators or pinholes are placed between the display screenand the optical sensor array in the under-screen optical sensor moduleto couple desired returned light from the display panel while filteringout background light in the optical detection by the optical sensorarray. Implementation of such optical collimators or pinholes cansimplify the optical designs of the optical detection by the opticalsensor array, e.g., without using complex optical imaging designs inother designs disclosed in this patent document, such as the imagingdesigns in FIGS. 6B, 7, 10A, and 11. In addition, implementation of suchoptical collimators or pinholes can simplify the optical alignment ofthe overall optical layout to the optical sensor array and improvereliability and performance of the optical detection by the opticalsensor array. Furthermore, such optical collimators or pinholes cansignificantly simplify the fabrication and reduce the overall cost ofthe under-screen optical sensor module.

FIG. 20 shows an under-screen optical sensor module that includes anoptical collimator array 2001 of optical collimators placed on top of aphotodetector array 2002 for directing signal light carrying fingerprintinformation into different photodetectors on the photodetector array2002. A circuitry module 2003 is coupled to the photodetector array 2002to operate the photodetector array 2002 and to receive the outputsignals from photodetectors on the photodetector array 2002. The OLEDdisplay module 433 includes small light transmission holes 82D, e.g.,holes in the TFT layer of the OLED display module, to allow the lightfrom the top surface of the top transparent layer 431 to pass throughthe OLED display module 433 to reach the under-screen optical sensormodule. The collimator array 2001 may use collimators in variousdesigns, e.g., waveguide based image transmitters, an optical fiberarray (with core or coreless), a micro lens array, a pinhole array andothers. The collimators in the array 2001 are designed to limit thenumerical aperture of the sampled image. Each pixel of the collimatorarray 2001 can be regarded as an optical detection needle. Thephotodiode array 2002 may be a CMOS sensor array, a CCD sensor array, aphotodiode array or other photosensing array.

In operation, the OLED pixels illuminate the cover glass 431. The lightreflected from the cover glass 431 is diffracted by the holes of the TFTstructure in the OLED display module 433. The collimator array 2001samples the useful part of the diffracted light and selects a portion ofthe light that fits the small numerical aperture of each collimator totransmit to the photodiode array 2002 to form the image of the sensingarea.

FIGS. 21A-21B show the operation of the optical sensor module in FIG.20. The OLED pixels in the illumination zone 613 in the OLED displaymodule 433 shine light beam 82P to the finger in contact with thesensing zone 615 on the cover glass 431. The finger and the cover glass431 reflect a light beam 82R. The small holes in the TFT substratediffract the light beam 82R to form light beam 82D. Proper collimatorunits in the collimator array 2001 select light 82S from the light beam82D and guide it into the proper photodetector elements of photodetectorarray 2002. In some OLED displays, part of the light may be directlyshined towards the sensor module and may be eliminated by calibration.

FIGS. 22A-22B show an exemplary implementation of the design in FIG. 20and FIGS. 21A-21B. The optical collimator array 2001 in this exampleincludes an array of optical collimators 903 and an optical absorptionmaterial 905 filled between the optical collimators 903 to absorb lightto reduce cross talk between different optical collimators. Eachcollimator 903 of the collimator array 2001 may be channels that areextended or elongated along a direction perpendicular to the displaypanel and lets the light be transmitted along its axis with a low loss.The collimator array 2001 is designed to reduce optical crosstalkbetween different optical collimators and to maintain a desired spatialresolution in the optical sensing. In some implementations, one opticalcollimator may correspond to only one photodetector in the photodetectorarray 2002. In other implementations, one optical collimator maycorrespond to two or more photodetectors in the photodetector array2002. As illustrated in FIG. 22B, the axis of each collimator unit maybe perpendicular to the display screen surface in some designs and maybe slanted with respect to the display surface. In operation, only thelight that propagates along a collimator axis carries the imageinformation. For example, the proper incident light 82P is reflected toform light 82R. Light 82R is then diffracted by the small holes of theTFT and expanded to light 82D. The light portion 82S is transmitted intothe photodiode array 2002. The light portion 82E away from the axis isabsorbed by the filling material. The reflectance on the cover glasssurface 431 carries the fingerprint information. Other OLED pixels emitlight 901 which is at an angle with respect to the collimator unit axisand thus may be blocked. A part of the reflected light, such as 901E,transmits into a corresponding optical collimator to reach thephotodetector array 2002.

The optical collimator array can be made by different techniques,including, e.g., etching holes through a flat substrate, forming a lightwaveguide array, forming a micro lens array matching with opticalfilters, using coreless optical fiber bundle, or printing collimators ona transparent sheet. The desired features for such a collimator arrayinclude: (1) sufficient transmission contrast between the lightcomponent that propagates along the axis and the component thatpropagates off the axis so that the collimators ensures the desiredspatial resolution in the optical sensing of the fingerprint pattern atthe photodetector array; (2) the permitted transmission numericalaperture be sufficiently small to realize a desired high spatialresolution for the optical sensing.

Various optical collimator array designs may be used. Each opticalcollimator in the optical collimator array is structured to performspatial filtering by transmitting light in directions along or close toan axis of the optical collimator while blocking light in otherdirections and to have a small optical transmission numerical apertureto achieve a high spatial resolution by the array of opticalcollimators. The small optical transmission numerical aperture alsoreduces the amount of the background light that enters the opticalsensor array. The collimator element aperture and the pitch (i.e., thedistance between two nearby collimator elements) can be designed toachieve a desired spatial resolution for the optical fingerprintsensing.

FIG. 23 shows an example of a collimator design that is part of the CMOSstructure by using aligned holes in two different metal layers in theCMOS structure. Each collimator in the array is an elongated channelalong a direction that is perpendicular to the display panel.

FIG. 24 shows an example of an optical fingerprint sensor module underthe OLED display structure that incorporates an optical sensor array andan integrated collimator array for each optical sensor pixel incapturing fingerprint information. The optical sensor array includes anarray of photodetectors and a collimator array is disposed over thephotodetector array to include optically transparent vias as opticalcollimators and optically opaque metal structures between the vias asshown. The OLED display pixels emit light to illuminate the touchedportion of a finger and the light reflected off the finger is directedthrough the collimator array to reach the photodetector array whichcaptures a part of the fingerprint image of the finger. The collimatorarray can be implemented using one or more metal layer(s) with holes oropenings integrated via the CMOS process.

Such optical collimators in the under-screen optical sensor module canbe structured to provide direct point to point imaging. For example, thedimensions of the optical collimator array and individual collimatorscan be designed to closely match the dimensions of the photodetectorarray and the dimensions of individual photodetectors, respectively, toachieve one to one imaging between optical collimators andphotodetectors. The entire image carried by the light received by theoptical sensor module can be captured by the photodetector array atindividual photodetectors simultaneously without stitching.

The spatial filtering operation of the optical collimator array canadvantageously reduce the amount of the background light that enters thephotodetector array in the optical sensor module. In addition, one ormore optical filters may be provided in the optical sensor module tofilter out the background light and to reduce the amount of thebackground light at the photodetector array for improved optical sensingof the returned light from the fingerprint sensing area due to theillumination by emitted light from the OLED pixels. For example, the oneor more optical filters can be configured, for example, as bandpassfilters to allow transmission of the light at emitted by the OLED pixelswhile blocking other light components such as the IR light in thesunlight. This optical filtering can be an effective in reducing thebackground light caused by sunlight when using the device outdoors. Theone or more optical filters can be implemented as, for example, opticalfilter coatings formed on one or more interfaces along the optical pathto the photodetector array in the optical sensor module or one or morediscrete optical filters.

FIG. 25 shows an example an optical collimator array with opticalfiltering to reduce background light that reaches the photodetectorarray in the under-screen optical sensor module. This example uses anarray of optical waveguides as the optical collimators and one or moreoptical filter films are coupled to the optical waveguide array toreduce undesired background light from reaching the photodetector arraycoupled to the optical waveguide array, e.g. the IR light from thesunlight while transmitting desired light in a predetermined spectralband for the probe light that is used to illuminate the finger. Theoptical waveguide can include a waveguide core with or without anoutside waveguide cladding. The optical waveguide may also be formed bya coreless fiber bundle with different fibers where each unit collimatoris a piece of fiber without a fiber core structure. When the corelessfibers are made into bundle, the filling material between the fibers mayinclude a light absorbing material so as to increase the absorption ofstray light that is not guided by the coreless fibers. The finalcollimator may be assembled with multiple layers of sub-collimatorarrays.

The following sections provide examples of various optical collimatordesigns and their fabrication.

FIGS. 26A and 26B show examples of fabricating collimators by etching.In FIG. 26A, a layer of a suitable material for forming opticalcollimators in the collimator array is formed on or supported by asupport substrate which is optically transparent. An etching mask isformed over the layer and has a pattern for etching the underlying layerto form the optical collimators. A suitable etching process is performedto form the optical collimators. The support substrate may be bound withthe collimator array and may be formed from various optical transparentmaterials including, e.g., silicon oxide.

FIG. 26B shows an example of an optical collimator array that isassembled by stacking multiple layers of sub-collimator arrays via aninter-layer connector material which may be an adhesive, a glass, or asuitable optically transparent material. In some implementations,different layers of sub-collimator arrays may be stacked over oneanother without the inter-layer connector material. This stacking allowsfabrication of optical collimators with desired lengths or depths alongthe collimator axis to achieve desired optical numerical apertures. Theholes of the collimators geometrically limit the viewing angle. Thetransmitting numeral aperture is decided by the thickness of thecollimator and the hole aperture. The holes may be filled with anoptically transparent material in some applications and may be void insome designs.

In implementations, the support substrate may be coated with one or moreoptical filter films to reduce or eliminate background light such as theIR light from the sunlight while transmitting desired light in apredetermined spectral band for the probe light that is used toilluminate the finger.

FIG. 27 shows an array of optical spatial filters coupled with microlens array where each microlens is located with respect to acorresponding through hole of an optical spatial filter so that eachunit collimator includes a micro lens and a micro spatial filter, suchas a micro hole. Each micro lens is structured and positioned to focusreceived light to the corresponding micro spatial filter without imagingthe received light. The micro hole limits the effective receivingnumerical aperture. The spatial filter may be printed on an opticallytransparent substrate, or etched on a piece of silicon wafer. The microlens array may be etched by MEMS processing or chemical processing. Themicro lens may also be made of a gradient refractive index material,e.g., cutting a piece of gradient refractive index glass fiber to aquarter pitch of length. The focal length of the micro lenses and thediameter of the spatial filter hole can be used to control thetransmitting numerical aperture of each unit. Like in other designs, thecollimator board may be coated with filter films to reduce or eliminatethe light band not used in the sensor such as the IR light from thesunlight.

FIG. 28 shows an example of an integrated CMOS photo detection arraysensor, with built-in collimation of light. The collimator is built bycombing an array of aligned holes (705) in different metal layers (704)and oxide layers (702,703) which are interleaved between metal layers toprovide separation. These holes can be aligned with photo sensitiveelements (701) in the optical sensor array. Optical fingerprint imageris implemented with this integrated CMOS photo detection array sensorwith built-in collimation of light under the OLED display module (710)and cover glass. The fingerprint of the user's finger touch the sensorwindow area of the cover glass can be imaged by detection of the lightreflected off the fingerprint valley and ridges, with the light emittingfrom the OLED display pixels of the window area. The light from afingerprint ridge area would be reduced, because the light is absorbedin fingerprint tissue at the ridge area while the light from thefingerprint valley area stronger by comparison. This difference in thelight levels between the ridges and valleys of a fingerprint produces afingerprint pattern at the optical sensor array.

In the above optical sensor module designs based on collimators, thethickness or length of each collimator along the collimator can bedesigned to be large to deliver imaging light to a small area on theoptical detector array or to be small to deliver imaging light to alarge area on the optical detector array. When the thickness or lengthof each collimator along the collimator in a collimator array decreasesto a certain point, e.g., tens of microns, the field of the optical viewof each collimator may be relatively large to cover a patch of adjacentoptical detectors on the optical detector array, e.g., an area of 1 mmby 1 mm. In some device designs, optical fingerprint sensing can beachieved by using an array of pinholes with each pinhole having asufficiently large field of optical view to cover a patch of adjacentoptical detectors in the optical detector array to achieve a high imageresolution at the optical detector array in sensing a fingerprint. Incomparison with a collimator design, a pinhole array can have a thinnerdimension and a smaller number of pinholes to achieve a desired highimaging resolution without an imaging lens. Also, different from theimaging via optical collimators, imaging with the array of pinholes useseach pinhole as a pinhole camera to capture the image and the imagereconstruction process based on the pinhole camera operation isdifferent that by using the optical collimator array: each pinholeestablishes a sub-image zone and the sub image zones by differentpinholes in the array of pinholes are stitched together to construct thewhole image. The image resolution by the optical sensor module with apinhole array is related to the sensitive element size of the detectorarray and thus the sensing resolution can be adjusted or optimized byadjusting the detector dimensions.

A pinhole array can be relatively simple to fabricate based on varioussemiconductor patterning techniques or processes or other fabricationmethods at relatively low costs. A pinhole array can also providespatial filtering operation to advantageously reduce the amount of thebackground light that enters the photodetector array in the opticalsensor module. Similar to designing the optical sensor modules withoptical collimators, one or more optical filters may be provided in theoptical sensor module with a pinhole array to filter out the backgroundlight and to reduce the amount of the background light at thephotodetector array for improved optical sensing of the returned lightfrom the fingerprint sensing area due to the illumination by emittedlight from the OLED pixels. For example, the one or more optical filterscan be configured, for example, as bandpass filters to allowtransmission of the light at emitted by the OLED pixels while blockingother light components such as the IR light in the sunlight. Thisoptical filtering can be an effective in reducing the background lightcaused by sunlight when using the device outdoors. The one or moreoptical filters can be implemented as, for example, optical filtercoatings formed on one or more interfaces along the optical path to thephotodetector array in the optical sensor module or one or more discreteoptical filters.

In an optical sensor module based on optical collimators, the opticalimaging resolution at the optical sensor array can be improved byconfiguring the optical collimators in a way to provide a pinhole cameraeffect. FIG. 29 shows an example of such a design.

In FIG. 29, a collimator unit 618 of an array of such opticalcollimators guides the light from the corresponding detection area unitto the photo detector array 621. The aperture of the collimator unitforms a small field of view (FOV) 618 b. If the detector in the photodetector array 621 does not capture the details in each unit FOV, theimaging resolution is decided by the FOV of each collimator unit. Toimprove the detection resolution, the FOV of each collimator unit needsto be reduced. However, when a gap 618 a is provided between each photodetector in the photo detector array 621 and the correspondingcollimator 618, the small aperture of the collimator unit acts as apinhole. This pinhole camera effect provides a higher imaging resolutionin the image of each unit of FOV. When there are multiple detectorelements in a unit FOV, such as shown in the insert 621 a, the imagesdetails in the unit FOV can be recognized. This means that the detectionresolution is improved. In implementations, such a gap can be providedin various ways, including, e.g., adding optical filter films 618 abetween the collimators 618 and the optical sensor array 621.

With the help of the pinhole camera effect, the fill factor of thecollimator board, may be optimized. For example, to detect an area of 10mm×10 mm in size, if each unit FOV covers an area of 1 mm×1 mm, a 10×10collimator array can be used. If in each unit FOV the detector can get20×20 definition image, the overall detection resolution is 200×200, or50 micron, or 500 psi. This method can be applied for all types ofcollimator approaches.

FIG. 30 shows another example for using the pinhole camera effect toimprove the optical imaging resolution. The OLED display module layer433 under the top transparent layer 431 includes, among others, OLEDlayers including an array of OLED pixels that emit light for displayingimages and have electrodes and wiring structure optically acting as anarray of holes and light scattering objects. The array of holes in theOLED layers is shown as small light transmitting holes 450 inside theOLED display module layer 433 and allows transmission of light from thetop transparent layer 431 through the OLED layers to reach the opticalsensor module 621 for fingerprint sensing. In this example, the opticalsensor module includes several layers: a spacer 917 below the OLEDdisplay module layer 433 and above the pinhole array 617, a protectionmaterial 919 below the pinhole array 617 and above the photo detectorarray 621, and a circuit board 623. The object optical distance isdecided by the total material thickness from sensing surface to thepinhole plane, including the optical thickness of the display module 433thickness, the spacer 917 thickness, any filter coating thickness, anyair gap thickness, and any glue material thickness. The image opticaldistance is decided by the total material thickness from the pinholeplane to the photo detector array, including the protection materialthickness, any filter coating thickness, any air gaps thickness, anyglue material thickness. The image magnification is decided by the imageoptical distance comparing with the object optical distance. Thedetection mode can be optimized by setting a proper magnification. Forexample, the magnification may be set to be less than 1, such as, 0.7,or 0.5 etc. In some device designs, the spacer and the pinhole arraylayer may be combined into a single component. In other designs, thepinhole array and the protection layer may be combined to a singlecomponent so as to pre-define the center co-ordinates of each pinhole.

FIG. 31A shows an example of the optical imaging based on the pinholecamera effect. On the object side, the whole detection zone 921 on theOLED display panel is divided into multiple sub-detection zones 923. Apinhole array 920 is provided for imaging the detection zone 921. Eachpinhole unit in the pinhole array 920 is responsible for a small fieldof view (FOV) 925. Each small FOV 925 covers a sub-detection zone 923.As shown in FIG. 31A, each small FOV of one pinhole can overlap withsmall FOVs of its neighboring pinholes. On the image side, eachsub-detection zone 923 in the optical sensor array captures an image933. Also shown in FIG. 31A, each small FOV 925 of a pinhole has acorresponding image zone 935. The magnification of this system can beoptimized so that the images of each sub-detection zone can beseparately distinguished. In other words, the images of the small FOVsdo not overlap each other. In this detection mode, the centralco-ordinates of each pinhole are pre-defined and the image spotco-ordinates of each OLED display pixel can be pre-calibrated. All thedisplay pixels in the detection zone can be lit on simultaneouslybecause each pixel has only one corresponding image position. Becausethe image of the pinhole camera is inversed, the signal processing canrecover the whole image based on the calibration table.

FIG. 32B shows an example of an under-screen optical sensor module byimplementing an array of optical pinholes to illustrate device designfactors that impact the field of the view (FOVi) produced by eachpinhole at the optical detector array and thus the imaging resolution ofthe optical sensor module. The illustrated example shows the thicknessvalues of relevant layers such as the total thickness (Ds) of the toptransparent layer 431 and the OLED display module layer 433, thethickness (T) of the layers 920 a for the pinhole array 920 a, thethickness (Di) of the protection material 919 below the pinhole array617 and above the photo detector array 621. As shown in FIG. 31B, thepinhole array 920 a is applied to image the sensing area where finger 60pressed upon the top sensing surface over the top transparent layer 433and the thickness T of the pinhole layers 920 a can affect the field ofview (FOV) angles. Together with the distances from the sensing surfaceto the pinhole and from the image plane to the pinhole, the sensing areaFOVs and imaging area FOVi are defined. The image magnification is givenby Di/Ds. In designing the device, the values of T, Ds, and Di can beadjusted and optimized to achieve a desired FOV and image magnification.

In the example in FIG. 31B, the neighboring FOVs can be adjusted tooverlap properly. Similarly, the neighboring FOVi can also be adjustedto be partially overlapped or fully separate or discrete from eachother. In a design that neighboring FOVs overlap each other, some of thespots on the sensing surface can have multiple image spots. This featurecan be used to enhance the optical detection of a fingerprint.

Either of the two background reduction techniques in FIGS. 12 and 13 maybe applied to the operation of the optical sensor module in FIG. 31B toreduce the background noise. For example, the display scan frame can beused to generate different frames of fingerprint signals. When twosequentially obtained frames of signals are obtained with the displaybeing lit on in one frame and being turned off in the other frame, thesubtraction of the two frames of signals can be used to reduce oreliminate the ambient background light influence as shown in FIG. 12 inwhich the fingerprint sensing frame rate is one half of the displayframe rate under this mode of operation.

In implementing the design in FIG. 31B and other designs for anunder-screen optical sensor module, optical filter films for reducingthe background light may be coated on the spacer 917, on the pinholelayers 920 a, on the protection layer 919 a, or on the display surfaces.As illustrated in FIG. 31B, when background light 937 is projected ontothe finger tissues 60, short wavelength components tend to be mostlyabsorbed by the finger tissues, a portion of the light in the longerwavelength (such as red light or infrared light) light transmits throughthe finger and propagates towards the optical detector array 621. Theoptical filter films can be used to reject those background lightcomponents at longer wavelengths to improve the optical detection of thefingerprint.

In the above illustrated examples for optical collimators, the directionof the optical collimators for directing light from a finger on the topof the display screen into the optical sensor array for fingerprintsensing may be either perpendicular to the top touch surface of OLEDdisplay screen to collect returned probe light from the finger forfingerprint sensing, a majority of which is in a light directionperpendicular to the top touch surface. In practice, when a touchedfinger is dry, the image contrast in the detected images in the opticalsensor array by sensing such returned probe light that is largelyperpendicular to the top touch surface is lower than the same imageobtained from returned probe light that is at an angle with respect tothe perpendicular direction of the top touch surface. This is in partbecause optical sensing of angled returned light spatially filters outthe strong returned light from the top touch surface that is mostlyperpendicular to the top touch surface. In consideration of this aspectof the optical sensing of the returned probe light from the top touchsurface, the optical collimators may be oriented so that the axis ofeach collimator unit may be slanted with respect to the top touchsurface as shown in the example in FIG. 22B.

In fabrication, however, it is more complex and costly to fabricateslanted collimators. One way to use perpendicular optical collimators asshown in FIGS. 20 and 21B while still achieving a higher contrast in theoptical sensing by selectively detecting angled returned light from thetop touch surface is to provide an optical deflection or diffractiondevice or layer between the perpendicular optical collimators and thereturned light from the top touch surface prior to entering theperpendicular optical collimators. This optical deflection ordiffraction device or layer can be, in some implementations, between theOLED display panel and the perpendicular optical collimators to selectonly returned probe light that is at some slanted angle to enter theperpendicular optical collimators for optical detection by the opticaldetector array on the other end of the perpendicular optical collimatorswhile blocking or reducing the amount of the returned probe light fromthe top touch surface that is perpendicular to the top touch surfacefrom entering the optical collimators. This optical deflection ordiffraction device or layer may be implemented in various forms,including, e.g., an array of prisms, an optical layer with a diffractionpattern, or other devices located between the optical collimators andthe display panel to select angled probe light returned from the displaypanel to enter the optical collimators while reducing an amount of thereturned probe light that is perpendicular to the display panel andenters the optical collimators.

FIG. 32 includes FIGS. 32A and 32B and shows an example of an opticalfingerprint senor under an OLED display panel having an opticaldeflection or diffraction device or layer.

As shown in FIG. 32A, each collimator 2001 in the collimator array maybe an extended channel along an axis vertical or perpendicular to thedisplay surfaces. A viewing angle adaptor optical layer 2210 is used toadjust the viewing angle of the returned probe light from the displaypanel and is located between the optical collimators 2001 and thedisplay panel to select angled probe light returned from the displaypanel to enter the optical collimators 2001 while reducing an amount ofthe returned probe light that is perpendicular to the display panel andenters the optical collimators 2001.

FIG. 32B shows more detail of the viewing angle adaptor optical layer3210 and the major probe light paths. For example, the viewing angleadaptor optical layer 3210 may be implemented as a diffraction patternlayer such as a prism structure 3210 a. Only the returned probe light 82a and 82 b from the finger with proper incident angles out of thedisplay panel can be bent to transmit through the collimator 2001. Incomparison, the returned probe light that is perpendicular to thedisplay panel is directed by the viewing angle adaptor optical layer2210 to be away from the original direction that is perpendicular to thedisplay panel and thus becomes off-axis incident light to the opticalcollimator 2001. This reduces the amount of the returned probe lightthat is perpendicular to the display panel and that can enter theoptical collimator 2001.

When the viewing angle is adjusted properly, the receiving light fromdifferent places 63 a and 63 b of the fingerprint valley carried thefingerprint information. For example, under same illumination, light 82a may be stronger than light 82 b because of the viewing angel and thefingerprint profiles of the fingertip skin. In other words, thedetection can see some level of fingerprint shade. This arrangementimproves the detection when the finger is dry.

Portable devices such as mobile phones or other devices or systems basedon the optical sensing disclosed in this document can be configured toprovide additional operation features.

For example, the OLED display panel can be controlled to provide a localflash mode to illuminate the fingerprint sensing area 613 by operatingselected OLED display pixels underneath the sensing area 613. This canbe provided in an optical sensor module under the OLED display panel,e.g., FIGS. 4A and 4B based on an optical imaging design or FIGS. 21Aand 21B based on optical imaging via an optical collimator array. In theevent of acquiring a fingerprint image, the OLED display pixels in thewindow area 613 can be turned on momentarily to produce high intensityillumination for optical sensing of a fingerprint, and, at the sametime, the photo detection sensor array 621 is turned on to capture thefingerprint image in sync with the turning on of the OLED pixelsunderneath the sensing area 613. The time to turn on these OLED pixelscan be relatively short but the emission intensity can be set to behigher than the normal emission for displaying images on the OLEDdisplay panel. For this reason, this mode for optical fingerprintsensing is a flash mode that enable the photo detector sensor array 621to detect a larger amount of light to improve the image sensingperformance.

For another example, the optical sensor module can be designed to meetthe total internal reflection condition at the top sensing surface ofthe OLED display panel to achieve a flash wakeup function where a partof the OLED pixels in the viewing zone 613 are turned on to flash whileother OLED pixels are tuned off and are in a sleep mode to save powerwhen the device is not in use. In response to the flashing of the OLEDpixels in the viewing zone 613, the corresponding photo sensors in theoptical sensor array 621 are operated to receive and detect lightsignals. When a finger touches the sensing zone 613 during this flashwakeup mode, the finger causes returned light to be totally reflected toproduce strong returned probe light which is detected at the opticalsensor array and the detection of the presence of light can be used towake up the device in the sleep mode. In addition to using the part ofOLED pixels in the viewing zone 613, one or more extra light sources maybe provided near the optical sensor module to provide the flash modeillumination at the viewing zone 613 for the flash wakeup function. Whena non-finger object touches the viewing zone 613 on the top surfaceabove the OLED display panel, the total internal reflection conditionmay not occur because other materials rarely have finger skinproperties. Therefore, even a non-finger object touches the sensing zone613, the lack of the total internal reflection at the touch location maycause insufficient returned probe light to reach the optical sensorarray to trigger flash wakeup operation.

The optical sensors for sensing optical fingerprints disclosed above canbe used to capture high quality images of fingerprints to enablediscrimination of small changes in captured fingerprints that arecaptured at different times. Notably, when a person presses a finger onthe device, the contact with the top touch surface over the displayscreen may subject to changes due to changes in the pressing force. Whenthe finger touches the sensing zone on the cover glass, changes in thetouching force may cause several detectable changes at the opticalsensor array: (1) fingerprint deforming, (2) a change in the contactingarea, (3) fingerprint ridge widening, and (4) a change in the blood flowdynamics at the pressed area. Those changes can be optically capturedand can be used to calculate the corresponding changes in the touchforce. The touch force sensing adds more functions to the fingerprintsensing.

Referring to FIG. 33, the contact profile area increases with anincrease in the press force, meanwhile the ridge-print expands with theincrease in the press force. Conversely, the contact profile areadecreases with a decrease in the press force, meanwhile the ridge-printcontracts or shrinks with the decrease in the press force. FIG. 33 showstwo different fingerprint patterns of the same finger under differentpress forces: the lightly pressed fingerprint 2301 and the heavilypressed fingerprint 3303. The returned probe light from a selectedintegration zone 3305 of the fingerprint on the touch surface can becaptured by a portion of the optical sensors on the optical sensor arraythat correspond to the selected integration zone 3305 on the touchsurface. The detected signals from those optical sensors are analyzed toextract useful information as further explained below.

When a finger touches the sensor surface, the finger tissues absorb thelight power thus the receiving power integrated over the photo diodearray is reduced. Especially in the case of total inner reflection modethat does not sense the low refractive index materials (water, sweatetc.), the sensor can be used to detect whether a finger touches thesensor or something else touches the sensor accidentally by analyzingthe receiving power change trend. Based on this sensing process, thesensor can decide whether a touch is a real fingerprint touch and thuscan detect whether to wake up the mobile device based on whether thetouch is a real finger press. Because the detection is based onintegration power detection, the light source for optical fingerprintsensing at a power saving mode.

In the detailed fingerprint map, when the press force increases, thefingerprint ridges expands, and more light is absorbed at the touchinterface by the expanded fingerprint ridges. Therefore within arelatively small observing zone 3305, the integrated received lightpower change reflects the changes in the press force. Based on this, thepress force can be detected.

Accordingly, by analyzing the integrated received probe light powerchange within a small zone, it is possible to monitor time-domainevolution of the fingerprint ridge pattern deformation. This informationon the time-domain evolution of the fingerprint ridge patterndeformation can then be used to determine the time-domain evolution ofthe press force on the finger. In applications, the time-domainevolution of the press force by the finger of a person can be used todetermine the dynamics of the user's interaction by the touch of thefinger, including determining whether a person is pressing down on thetouch surface or removing a pressed finger away from the touch surface.Those user interaction dynamics can be used to trigger certainoperations of the mobile device or operations of certain apps on themobile device. For example, the time-domain evolution of the press forceby the finger of a person can be used to determine whether a touch by aperson is an intended touch to operate the mobile device or anunintended touch by accident and, based on such determination, themobile device control system can determine whether or not to wake up themobile device in a sleep mode.

In addition, under different press forces, a finger of a living personin contact with the touch surface can exhibit different characteristicsin the optical extinction ratio obtained at two different probe lightwavelengths as explained with respect FIGS. 14A and 14B. Referring backto FIG. 33, the lightly pressed fingerprint 3301 may not significantlyrestrict the flow of the blood into the pressed portion of the fingerand thus produces an optical extinction ratio obtained at two differentprobe light wavelengths that indicates a living person tissue. When theperson presses the finger hard to produce the heavily pressedfingerprint 3303, the blood flow to the pressed finger portion may beseverely reduced and, accordingly, the corresponding optical extinctionratio obtained at two different probe light wavelengths would bedifferent from that of the lightly pressed fingerprint 3301. Therefore,the optical extinction ratios obtained at two different probe lightwavelengths vary under different press forces and different blood flowconditions. Such variation is different from the optical extinctionratios obtained at two different probe light wavelengths from pressingwith different forces of a fake fingerprint pattern of a man-madematerial.

Therefore, the optical extinction ratios obtained at two different probelight wavelengths can also be used to determine whether a touch is by auser's finger or something else. This determination can also be used todetermine whether to wake up the mobile device in a sleep mode.

For yet another example, the disclosed optical sensor technology can beused to monitor the natural motions that a live person's finger tends tobehave due to the person's natural movement or motion (either intendedor unintended) or pulsing when the blood flows through the person's bodyin connection with the heartbeat. The wake-up operation or userauthentication can be based on the combination of the both the opticalsensing of the fingerprint pattern and the positive determination of thepresence of a live person to enhance the access control. For yet anotherexample, the optical sensor module may include a sensing function formeasuring a glucose level or a degree of oxygen saturation based onoptical sensing in the returned light from a finger or palm. As yetanother example, as a person touches the display screen, a change in thetouching force can be reflected in one or more ways, includingfingerprint pattern deforming, a change in the contacting area betweenthe finger and the screen surface, fingerprint ridge widening, or ablood flow dynamics change. Those and other changes can be measured byoptical sensing based on the disclosed optical sensor technology and canbe used to calculate the touch force. This touch force sensing can beused to add more functions to the optical sensor module beyond thefingerprint sensing.

The above optical sensor module designs and features are directed tocollecting optical signal to the optical detectors in an under-screenoptical sensor module and providing desired optical imaging quality(e.g., the detected image resolution) via an optical imaging byimplementing at least one imaging lens or an array of collimators orpinholes. As mentioned above, background reduction techniques may beprovided in an under-screen optical sensor module by performing certaincontrols and signal processing such as the two examples shown in FIGS.12 and 13. In addition, one or more additional optical design featuresmay be added to the above disclosed optical sensor module designs toreduce the background light based on background light filtering oradding extra illumination light sources. The different background lightreduction techniques based on operation control/signal processing,optical filtering and adding extra illumination light sources can becombined in various ways in implementations.

The optical filtering technique for reducing the background light can beimplemented in various optical sensor module designs disclosed in thisdocument. While the general goal of inserting optical filters in theoptical path of the optical sensor module is to reject the environmentlight wavelengths, such as near IR and partial of the red light andother undesired wavelengths, the specific implementation of such opticalfilters can vary based on the specific needs of each application. Suchoptical filters can be formed by forming optical filter coatings onselected surfaces of the optical parts in the optical path leading tothe optical detector array 621, including, e.g., the display bottomsurface, surfaces of other optical components such as optical prisms,the up sensor surface of the optical detector array 621, etc. Forexample, human fingers absorb most of the energy of the wavelengthsunder a certain wavelength (e.g., around ˜580 nm), if the opticalfilters are designed to reject the light in the wavelengths from thiswavelength around ˜580 nm to infrared, the undesired environment lightinfluence can be greatly reduced.

FIG. 34 shows an example of the optical transmission spectral profilesof a typical human thumb and litter finger at several different opticalwavelengths from around 525 nm to around 940 nm. For short wavelengths,such as wavelengths less than 610 nm, less than 0.5% of theenvironmental light may pass through the finger. Red light and near IRlight have higher transmission. The transmission of the environmentallight through a finger goes to a wide range of directions due toscattering by the finger tissues and thus can mix with the signal lightto be detected by the under-screen optical sensor module. When operatedunder the sunlight, the undesired environmental light from the sunlightmust be handled carefully due to the high optical power of the sunlightto reduce or minimize the adverse impact to the optical fingerprintsensor performance.

FIG. 35 illustrates influences of the background light in anunder-screen optical sensor module 600 a. The undesired environmentallight that can adversely affect the optical fingerprint sensing may passthrough different paths to reach the optical fingerprint sensor 600 a.In some cases, the environmental light paths can be divided intodifferent situations based on their optical paths: some light like 937passes through the finger to enter the optical fingerprint sensor 600 a,and some light like 937 a does not pass through the finger but entersthe optical fingerprint sensor 600 a from one or more sides around thefinger.

In the illustrated under-screen optical sensor module 600 a forfingerprint sensing, a sensor package 600 b is formed outside theunder-screen optical sensor module 600 a and may be formed of an opticalopaque or absorptive material as a background blocker, at least for someof incident background light such as part large angled light in thebackground light like 937 a that does not pass through the finger butenters the optical fingerprint sensor 600 a from one or more sidesaround the finger.

With respect to the environmental light 937 that propagates through thefinger 60 a, the finger 60 a absorbs some of the incident light so thatpart of the light 939 transmits through the finger 60 a to reach thecover glass 431, and subsequently transmits through the cover glass 431to reach the OLED TFT layers. The small holes 450 in the OLED TFT layersblock most of such background light but a small portion of light 941 ofsuch background light 939 passes through the small holes 450 to enterinto the optical fingerprint sensor package 600 a/600 b.

Some of the environmental light 937 a propagates directly to the coverglass 431 by transmitting through the finger. Such transmitted light isrefracted into the cover glass 431 and becomes light 939 a. The OLED TFTlayers small holes 450 allow a small part of light 941 a to pass throughto reach the optical fingerprint sensor package 600 a/600 b. Thiscomponent of environmental light tends to include light components withlarge incident angles. The detection light paths can be designed so thatthis part of environmental light does not mix with the signal light.

The optical fingerprint sensor package can be designed to cause theoptical sensor module 600 a to receive only light from the detectionlight path window while blocking undesired environmental light at largeincident angles. For example, in some implementations, the OLED lightsource of an OLED display can be used as the probe light source forilluminating the finger for optical fingerprint sensing. Under thisdesign, only the top side of the optical sensor module 600 a that isengaged to (e.g., being glued) the bottom of the OLED display module isopen to receive light, such as the optical window 600 c on the top ofthe optical fingerprint sensor package shown in FIG. 35 and the sensorbottom and side walls are not optically transparent within the detectionlight wavelength band so that the environmental light that can enter theoptical fingerprint sensor is reduced. Therefore, for the environmentallight that enters into the optical sensor module without firsttransmitting through the finger, the packaging of the optical sensormodule can be designed to provide absorption or blockage of such lightwith light blocking side walls or properly designed optical receivingaperture so that such light, when reaching to the receiving opticsmaterial or the package material, is absorbed or blocked.

The undesired environmental light can include different wavelengthcomponents and thus such different environmental light components shouldbe handled differently to reduce their impacts to the opticalfingerprint sensing in implementing the disclosed technology.

For example, the undesired environmental light may include lightcomponents that transmit through the finger in the red (e.g., longerthan 580 nm) and longer wavelengths and light components that do nottransmit through the finger in the shorter wavelengths than the redwavelengths (e.g., less than 580 nm). Due to this wavelength-dependentabsorption of the finger, the transmitted environmental light throughthe finger usually includes some near IR and partial of the red lightcomponent. Therefore the optical filtering can be included in theoptical fingerprint sensor package to filter out the undesiredenvironmental light that would otherwise enter the optical detectorarray.

An example design is to use one or more IR blocking filter coatings,e.g., an IR-cut filter coating, to reduce the IR or near IR light in thetransmitted light from the finger. However, various IR-cut filters usedfor imaging devices normally only restrict wavelengths greater than 710nm. When a device is exposed to direct or indirect sunlight, thisfiltering performance may not be good enough for reducing IR backgroundlight in optical fingerprint sensing. Suitable IR filtering coatingsshould extend the short end cut-off wavelength to shorter wavelengthsbelow 710 nm, for example, 610 nm, in some applications.

Due to the spectral responses of various IR cut coatings, a single IRcut filter with an extended working band to shorter wavelengths may notprovide the desired IR blocking performance. In some filter designs forthe under-screen optical sensor module, two or more optical filters maybe used in combination to achieve the desired IR blocking performance inthe sensor light paths. This use of two or more filters is in partbecause one significant technical issue is the strong background lightfrom the natural day light from the sun. In the examples of disclosedoptical sensors under the OLED display panel, an optical filteringmechanism can be built into the under-screen optical sensor stack toblock or reduce the strong background light from the natural day lightfrom the sun that enters the optical sensor array 600 a. Accordingly,one or more optical filter layers may be integrated into theunder-screen optical sensor stack above the optical sensor array toblock the undesired background day light from the sun while allowing theillumination light for the optical fingerprint sensing to pass throughto reach the optical sensor array.

For example, the illumination light may be in the visible range from theOLED emission for the display, e.g., from 400 nm to 650 nm, in someimplementations and the one or more optical filters between the OLEDpanel and the optical sensor array can be optically transmissive tolight between 400 nm and 650 nm while blocking light with opticalwavelengths longer than 650 nm, including the strong IR light in the daylight. In practice, some commercial optical filters have transmissionbands that may not be desirable for this particular application forunder screen optical sensors disclosed in this document. For example,some commercial multi-layer bandpass filters may block light above 600nm but would have transmission peaks in the spectral range above 600 nm,e.g., optical transmission bands between 630 nm and 900 nm. Strongbackground light in the day light within such optical transmission bandscan pass through to reach the optical sensor array and adversely affectthe optical detection for optical fingerprint sensing. Those undesiredoptical transmission bands in such optical filters can be eliminated orreduced by combining two or more different optical filters together withdifferent spectral ranges so that undesired optical transmission bandsin one filter can be in the optical blocking spectral range in anotheroptical filter in a way that the combination of two or more such filterscan collectively eliminate or reduce the undesired optical transmissionbands between 630 nm to 900 nm. Specifically, for example, two opticalfilters can be combined by using one filter to reject light from 610 nmthrough 1100 nm while transmitting visible light below 610 nm inwavelength and another filter to reject light in a shifted spectralrange from 700 nm through 1100 nm while transmitting visible light under700 nm in wavelength. This combination of two or more optical filterscan be used to produce desired rejection of the background light atoptical wavelengths longer than the upper transmission wavelength. Suchoptical filters may be coated over the spacer 917, collimator 617,and/or protection material 919 shown various examples, including FIG.31B.

In some implementations, when using two or more optical filters asdisclosed above, an optical absorbing material can be filled between thetwo filters to exhibit proper absorption for the rejected light band sothat the bouncing light between the two optical filters can be absorbed.For example, one filter may be coated on spacer 917, and the otherfilter be coated on protection material 919, while the collimator 617can be made optically absorbing to absorb the rejected light band by thetwo filters. As a specific example, a piece of blue glass that has highabsorption from 610 nm to 1100 nm can be used as base of the filters. Inthis case the two filters are coated on up and down surfaces of the blueglass, and this component can be used as the spacer or the protectionmaterial.

In addition to using proper optical filtering for cutting backgroundlight in the red and IR ranges in an under-screen optical sensor module,the background light that should be reduced by the optical filtering mayinclude light in the shorter wavelength spectral ranges including the UVwavelengths. In some implementations, the environmental light in the UVband should be reduced or eliminated because this band of light generatenoises. This elimination can be realized by UV-cut off coating or bymaterial absorption. Finger tissues, silicon, and black oil ink andothers tend to absorb the UV light strongly. The material absorption ofUV light can be used to reduce the UV light influence to the opticalfingerprint sensing.

FIG. 36 shows an example of a design algorithm for designing the opticalfiltering in an under-screen optical sensor module in light of the abovediscussions for reducing background light. Hence in addition todesigning proper optical filters in the optical path to the opticalsensor module, additional design features for reducing the backgroundlight can be added to the design of the receiving optics for the opticaldetector array in the optical sensor module. Those optical filteringconsiderations and the further background light reduction via operationcontrol and signal processing in operating such an optical sensor modulecan be combined to achieve the desired optical sensing performance.

In an under-screen optical sensor module having an optical collimatorarray or an optical pinhole array before the optical detector array, theoptical collimator array or optical pinhole array is part of thereceiving optics and can be designed with a small optical numericalaperture to reduce the background light that enters the optical detectorarray. FIG. 37 shows two examples in FIGS. 37A and 37B.

Referring to FIG. 37A, the collimator pinhole 951 can be designed to beoptically transparent within the probe light band, the collimator wallmaterials 953 can be selected to absorb the light 955 that reaches thewall. If the collimator material is silicon, a blackened, lightabsorbing coating can be formed on each wall.

Referring to FIG. 37B, the pinhole array of pinholes 959 as part of thereceiving optics can be constructed to have an effective numeralaperture to block the environmental light with large incident angles. Alight blocking layer with an array of aperture restriction holes 961 maybe formed below the array of the pinholes 959 so that the light 967 outof the effective numeral aperture can be blocked by the opaque sectionof the light blocking layer with the aperture restriction holes 961. Thematerials 963 and 965 that form the imaging camera pinholes 959 and theaperture restriction holes 961 can an optically opaque material oroptically absorbing material such as a black oil ink, or an opticalreflection material such as a metal film.

In some implementations, one or more optical filters may be used as thesubstrate for supporting the pinhole camera type optics so that multiplefunctional parts can be combined or integrated into one piece ofhardware. This integration or combination of different background lightreduction mechanism can reduce the device cost and may also reduce thedevice thickness.

An under-screen optical sensor module may also be operated with a sensorinitialization process to reduce undesired influences of the backgroundlight. Like the techniques shown in FIGS. 12 and 13, this sensorinitialization process is operational in nature. FIG. 38 illustrates anexample of this sensor initialization process that measures a baselinebackground level at the optical sensor array each time a fingerprint isobtained. Before preforming the actual fingerprint sensing, in a darkroom environment without any environmental light influence, theillumination light or the optical probe light for the optical sensing(the OLED display) is turned on, a finger simulator device is placed onthe cover glass to record the image data. The finger simulator device isdesigned to simulate the finger skin reflection behavior but does nothave any fingerprint pattern. This image data obtained from the fingersimulator device is saved into memory as the base 1 data for thebackground light reduction processing in real sensing operations. Thisprocess can be a device calibration process done in factory beforeshipping the device.

In real time fingerprint sensing, the environmental influence ispresent. In operation, the illumination light or the optical probe light(e.g., the OLED screen) is first turned off to record the image data asbase 2, which is made under a condition with the environmental light.This base₂ represents the total influence of all the environmental lightresidues. The sum of base 1 and base 2 gives the real-time base. Next,the illumination light or optical probe light is turned on to performfingerprint sensing to capture a real-time signal which is a mixture ofthe real fingerprint signal from the fingerprint and the real-time base.A differential between the signal mixture and the real-time base can beperformed as part of the signal processing to reduce the signalcontribution by the environmental light so that the image quality of thefingerprint image can be obtained. The above example in FIG. 38illustrates a method for operating an electronic device capable ofdetecting a fingerprint by optical sensing by operating an opticalsensor module located below a touch display panel, that provides touchsensing operations for the device, to produce probe light to theilluminate a top transparent layer of the touch display panel to operatean optical sensor array inside the optical sensor module to obtain afirst image from returned probe light from the top transparent layer.This method includes operating the optical sensor array inside theoptical sensor module, while turning off the probe light, to obtain asecond image under illumination with only environmental light withoutilluminating the top transparent layer of the touch display panel withany probe light; and processing the first image and the second image toremove an effect from the environmental light in an imaging operation ofthe device.

Based on the above, the undesired effect of the background light to theperformance the under-screen optical sensor module can be mitigated indifferent techniques, including implementing optical filtering in theoptical path to the optical sensor array to reduce the background light,designing the receiving optics for the optical sensor array to reducethe background light, or controlling the operations of the opticalsensor module and signal processing to further reduce the effect of thebackground light to the optical sensing performance. Those differenttechniques may be used individually or in combination to meet thedesired device performance.

In the disclosed optical sensing technology, in addition to using theOLED-emitted light from the OLED display module, one or more extra lightsources can be used to illuminate the finger to be detected to improvethe optical fingerprint sensing, e.g., by improving the signal to noiseratio in the detection. This inclusion of one or more extra illuminationlight sources to increase the optical signal level of the opticalsensing signal carrying the fingerprint or other useful informationbeyond the signal level caused by the returned OLED display light forimproving the optical sensing sensitivity can be used alone or in acombination with above disclosed techniques for reducing the amount ofbackground light that enters the optical sensor array in an under-screenoptical sensor module.

In this regard, an electronic device capable of detecting a fingerprintby optical sensing can be designed to include a device screen thatprovides touch sensing operations and includes a display panel structurehaving light emitting display pixels where each pixel is operable toemit light for forming a portion of a display image, a top transparentlayer formed over the device screen as an interface for being touched bya user for the touch sensing operations and for transmitting the lightfrom the display structure to display images to a user, and one or moreextra illumination light sources located to provide additionalillumination light to the top transparent layer formed over the devicescreen as the interface for being touched by a user. Such a device canfurther include an optical sensor module located below the display panelstructure to receive light that is emitted by at least a portion of thelight emitting display pixels of the display structure and by the one ormore extra illumination light sources and is returned from the toptransparent layer to detect a fingerprint, the optical sensor moduleincluding an optical sensor array that detects an image in the receivedlight in the optical sensor module. In implementations, such as invarious OLED screens, the display panel structure includes openings orholes between the light emitting display pixels of the display panelstructure to allow the returned light to pass through the display panelstructure to reach the optical sensor module, and the optical sensormodule includes an array of optical collimators or an array of pinholesto collect the returned light from the display panel structure and toseparate light from different locations in the top transparent layerwhile directing the collected returned light to the optical sensorarray.

The first example for using extra illumination lighting is shown FIG. 9which includes one or more extra light sources 614 that are attached toor glued into the same position or region of the viewing zone 613 toprovide additional illumination to the sensing zone 615, thus increasingthe light intensity in optical sensing operations. The extra lightsources 614 may be of an expanded type, or be a collimated type so thatall the points within the effective sensing zone 615 is illuminated. Theextra light sources 614 may be a single element light source or an arrayof light sources. Furthermore, the OLED pixels in the viewing zone orthe fingerprint illumination zone 613 in the OLED display module 433 maybe operated a higher brightness level during the optical fingerprintsensing operation above the brightness level used for displaying imagesin the OLED display to boost the illumination level for the opticalsensing operation.

FIGS. 39 and 40 show optical behaviors of various optical signals in anexample of an under-screen optical sensor module having extraillumination light sources to supplement the optical fingerprint sensingillumination provided by the OLED display light.

The example in FIGS. 39 and 40 includes extra light sources 971 that areassembled in the optical sensor module. Specifically, two or more extralight sources 971 are placed outside the optical sensor module 600 a andare outside the packaging walls 600 b. Each extra light source 971 maybe one light source or include multiple sources, for example, LED lightsources. The extra light sources 971 may be operable to emit light atone single wavelength or at multiple wavelengths (for example, greenLED, red LED, near IR LED). The extra light sources 971 may be modulatedto produce modulated illumination light or be operated to turn on theiremission at different phases. At the output port of each extra lightsource 971, a proper coupling material 972 is provided between eachextra light source 971 and the OLED display module. The couplingmaterial 972 may include a suitable optically transparent material toallow the probe light 973 from the extra light source 971 to be coupledinto the display towards the finger on the cover 431 surface. In someimplementations, it may be desirable to avoid large output angles of theprobe light 973 in the display and the coupling material 972 may beconfigured to limit the probe light's numeral aperture. The couplingmaterial 972 may be a low index material such as an air gap and may bestructured to have a desired output aperture that limits the outputangle of the probe light 973 in the display.

The small holes 450 in the TFT layers of the OLED display module scatterthe probe light beam 973 into various directions. As shown in FIG. 39,some scattered light 977 propagates towards the optical sensor module660 a at large angles and is less likely to enter the optical sensormodule due to the absorption or blocking by the small aperture of thereceiving optics of the optical sensor module 660 a. Some scatteredlight 977 a propagates towards other directions that are away from theaperture of the optical sensor module 660 a and thus does not affect theoptical sensing. Notably, a portion of the probe light 973 from eachextra light source 971 passes through the TFT layers as the probe light975 towards the top surface of the top transparent layer 431. This probelight 975 can be coupled into the finger 60 a. The tissues in the finger60 a scatter the probe light 975 to produce scattered probe light 979 invarious directions, including back scattered probe light 981. The backscattered probe light 981 propagates back through the top transparentlayer 431 to enter the TFT layers towards the optical sensor module 600a. The TFT layers refract or scatter the back scattered probe light 981,a portion of which becomes the probe light component 983 that can bedetected by the photo-detector array in the optical sensor module 600 a.

When the probe light 979 propagates through the finger skin, thefingerprint ridge area and valley area manifest light signals withdifferent brightness and this brightness contrast forms the fingerprintpattern and is caused by the finger tissue absorption, refraction, andreflection, by finger skin structure shading, and by reflectancedifference at the finger skin-display cover glass interface. Because ofthe complicated mechanism of the fingerprint contrast, the fingerprintcan be detected even if the finger is dry, wet, or dirty.

FIG. 40 further shows that background light present at the device cangenerally include two different portions the environmental or backgroundlight 937 incident to the finger 60 a and environmental or backgroundlight 937 c incident to the top transparent layer 431 without enteringthe finger 60 a. Since the environmental or background light 937propagates into finger 60 a, the finger tissues scatter the receivedbackground light 937 as scattered background light 937 b in differentdirections and mixes with the probe light 979. Some of the scatteredlight 939 in the scattered background light 937 b propagates backtowards the optical sensor module 600 a through the finger 60 a. Thescattered background light 939 and a portion of the environmental light937 c that does not go through the finger 60 a and enters the opticalsensor module 600 a adversely impact the optical sensing operation ofthe optical sensor module 600 a. Therefore, it is desirable to reduce oreliminate the amount of the environmental light from entering theoptical sensor module 600 a by optical filtering, by the design of thereceiving optics or by controlling the operation and signal processingof the optical sensor module as discussed above with reference to FIGS.36-38.

FIG. 41 shows an example of a design algorithm for designing the opticalfiltering in an under-screen optical sensor module with extra lightsources for optical sensing. The considerations for the design in FIG.41 are to reduce or eliminate the environmental light at the opticalsensor module, including environmental light that transmits through thefinger and that does not transmit through the finger. This is similar tothe design shown in FIG. 36. Because the absorption of the finger, thetransmitted environmental light include some near IR and partial of thered light component. Therefore the optical filter coatings should bedesigned to handle the remained environmental light. An example designis to use RED/IR band pass filtering since the red and near IR light cantravel into relatively long distances in finger tissues. Consideringthat the sunlight is strong, the band pass filter can be designed basedon the probe light source wavelength band. As discussed above inconnection with FIG. 36, the UV band should also be eliminated becausethis band of light generate noises. This elimination can be realized byUV-cut off coating or by material absorption. Finger tissue, silicon,and black oil ink etc. absorbs UV light strongly. In some designs, thematerial absorption may be used to eliminate the UV light influence. Forthe environmental light that does not transmit through the finger, theextinction may be achieved by designing the receiving optics absorption.This part of light features large incident angles that can be blocked bythe properly designed receiving numeral aperture.

The techniques for reducing the background light in FIGS. 37 and 38 canalso be applied to the optical sensor module with extra light sourcesfor optical sensing in FIGS. 39 and 40 for reduction of theenvironmental light.

When extra light sources are provided for optical sensing, theillumination power for optical sensing is no longer limited by theoptical power from the OLED display light. Such extra light sources canbe designed to provide sufficient illumination for optical sensing toimprove the optical detection signal to noise ration to offset theenvironmental light influence. In implantations, the extra light sourcescan be modulated without affecting the display function and lifetime. Inaddition, the extra light sources can be flashed with high output powerfor a short time during the fingerprint sensing so as to obtainoptimized detection. In addition, the use of extra light sources canprovide flexibility in the determination of whether a detected finger isa live finger so that fake fingerprint detection can be avoided. Forexample, green LEDs and near IR LEDs may be used as extra light sourcesto also assist the live finger detection as explained with reference toFIGS. 14A and 14B where finger tissues absorb the green light stronglyso that the finger image manifests a desired large brightness gradientand the near IR light illuminates all through the finger so that thefinger image brightness appears more uniform.

While this patent document contains many specifics, these should not beconstrued as limitations on the scope of any invention or of what may beclaimed, but rather as descriptions of features that may be specific toparticular embodiments of particular inventions. Certain features thatare described in this patent document in the context of separateembodiments can also be implemented in combination in a singleembodiment. Conversely, various features that are described in thecontext of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Moreover, the separation of various system components in theembodiments described in this patent document should not be understoodas requiring such separation in all embodiments.

Only a few implementations and examples are described and otherimplementations, enhancements and variations can be made based on whatis described and illustrated in this patent document.

What is claimed is:
 1. An optical sensor module, for being arrangedunder a display panel to capture a fingerprint pattern of a finger abovethe display panel, the optical sensor module comprising: an opticalsensor array of optical detectors for receiving probe light that isreturned from the finger and carrying fingerprint information, andconverting the probe light into detector signals representing afingerprint pattern, wherein the returned probe light is generated whenthe finger is illuminated and is transmitted through the display panel;and an array of optical collimators located between the display paneland the optical sensor array, for collecting angled probe light returnedfrom the display panel, and directing the angled probe light to thecorresponding optical detectors of the optical sensor array; wherein theoptical sensor module is structured to measure probe light at two ormore different wavelengths to compare characteristics of the probe lightat the two or more different wavelengths to determine of whether theprobe light is from a live person, the probe light at two or moredifferent wavelengths correspond to light emitted by light emittingdisplay pixels in the display panel, and the characteristics of theprobe light at the two or more different wavelengths comprises anextinction ratio of the probe light at the two or more differentwavelengths.
 2. The optical sensor module as in claim 1, wherein thearray of optical collimators and spacing between the array of opticalcollimators and the optical sensor array are structured to cause imagesof a field of view of the optical collimators at the optical sensorarray to be spatially separated.
 3. The optical sensor module as inclaim 1, wherein the optical collimators has an optical axis that isslanted with respect to the display panel, so that the angled probelight returned from the display panel is capable of passing through theoptical collimators and reaching the optical detectors of the opticalsensor array.
 4. The optical sensor module as in claim 3, wherein thearray of optical collimators is built by combing an array of alignedholes in different light block layers and transparent layers which areinterleaved between the light block layers to provide separation.
 5. Theoptical sensor module as in claim 4, wherein the light block layers aremetal layers, and the transparent layers are oxide layer.
 6. The opticalsensor module as in claim 5, wherein an aperture of the aligned holes ina metal layer is different from that in another metal layer.
 7. Theoptical sensor module as in claim 4, further comprising: a micro lensarray comprising a plurality of micro lenses arranged on the array ofoptical collimators, wherein each micro lens is located with respect toa corresponding optical collimator.
 8. The optical sensor module as inclaim 1, further comprising: an optical layer between the opticalcollimators and the display panel to select the angled probe lightreturned from the display panel to enter the optical collimators whilereducing an amount of the probe light that is perpendicular to thedisplay panel and enters the optical collimators.
 9. The optical sensormodule as in claim 8, wherein the optical layer comprises an opticaldiffraction pattern that diffracts the probe light to direct the angledprobe light returned from the display panel to enter the opticalcollimators.
 10. The optical sensor module as in claim 8, wherein theoptical collimators has an optical axis perpendicular to the displaypanel, and the optical layer between the optical collimators and thedisplay is structured to direct the angled probe light from the displaypanel to be substantially perpendicular to the display panel to enterthe optical collimators while directing a portion of the probe lightfrom the display panel that is perpendicular to the display panel to beaway from the direction of the optical collimators.
 11. An opticalsensor module, for being arranged under a display panel to capture afingerprint pattern of a finger above the display panel, the opticalsensor module comprising: an optical sensor array of optical detectorsfor receiving probe light that is returned from the finger and carryingfingerprint information, and converting the probe light into detectorsignals representing a fingerprint pattern, wherein the returned probelight is generated when the finger is illuminated and is transmittedthrough the display panel; and an array of optical collimators locatedbetween the display panel and the optical sensor array, for collectingangled probe light returned from the display panel, and directing theangled probe light to the corresponding optical detectors of the opticalsensor array; wherein the optical collimators has an optical axis thatis slanted with respect to the display panel, so that the angled probelight returned from the display panel is capable of passing through theoptical collimators and reaching the optical detectors of the opticalsensor array; and wherein the array of optical collimators is formed bycombing an array of aligned holes in different metal layers andinsulating layers which are interleaved between the light block layersto provide separation; wherein an aperture of the aligned holes in ametal layer is different from that in another metal layer, and a microlens array comprising a plurality of micro lenses arranged on the arrayof optical collimators, wherein each micro lens is located with respectto a corresponding optical collimator.
 12. The optical sensor module asin claim 11, wherein the optical sensor module is further structured tomeasure probe light at two or more different wavelengths to comparecharacteristics of the probe light at the two or more differentwavelengths to determine of whether the probe light is from a liveperson.
 13. The optical sensor module as in claim 11, wherein theoptical sensor module is further structured to capture differentfingerprint patterns at different times to monitor time-domain evolutionof the fingerprint ridge pattern deformation that indicates time-domainevolution of a press force from the finger.
 14. The optical sensormodule as in claim 11, wherein the array of optical collimators andspacing between the array of optical collimators and the optical sensorarray are structured to cause images of a field of view of the opticalcollimators at the optical sensor array to be spatially separated. 15.The optical sensor module as in claim 1, wherein the optical sensormodule is further structured to capture different fingerprint patternsat different times to monitor time-domain evolution of the fingerprintridge pattern deformation that indicates time-domain evolution of apress force from the finger.